Something that is unstable or subject to change can be described as fluid. The fluid political situation in a particular country makes it unsafe to travel there, with the constant possibility of a violent uprising.

A liquid is a fluid — something that flows easily when poured — although gases can also be called fluid. When your doctor told you to drink lots of fluids to help your cold symptoms, she probably meant things like water or orange juice, not root beer floats. If a movement is smooth, it can also be described as fluid. You have to make fluid arm movements in ballet so you look graceful.

Definitions of fluid
  1. noun
    continuous amorphous matter that tends to flow and to conform to the outline of its container: a liquid or a gas
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    a fluid in the gaseous state having neither independent shape nor volume and being able to expand indefinitely
    fluid matter having no fixed shape but a fixed volume
    the envelope of gases surrounding any celestial body
    argonon, inert gas, noble gas
    any of the chemically inert gaseous elements of the helium group in the periodic table
    Cl, atomic number 17, chlorine
    a common nonmetallic element belonging to the halogens; best known as a heavy yellow irritating toxic gas; used to purify water and as a bleaching agent and disinfectant; occurs naturally only as a salt (as in sea water)
    F, atomic number 9, fluorine
    a nonmetallic univalent element belonging to the halogens; usually a yellow irritating toxic flammable gas; a powerful oxidizing agent; recovered from fluorite or cryolite or fluorapatite
    H, atomic number 1, hydrogen
    a nonmetallic univalent element that is normally a colorless and odorless highly flammable diatomic gas; the simplest and lightest and most abundant element in the universe
    N, atomic number 7, nitrogen
    a common nonmetallic element that is normally a colorless odorless tasteless inert diatomic gas; constitutes 78 percent of the atmosphere by volume; a constituent of all living tissues
    O, atomic number 8, oxygen
    a nonmetallic bivalent element that is normally a colorless odorless tasteless nonflammable diatomic gas; constitutes 21 percent of the atmosphere by volume; the most abundant element in the earth's crust
    occurs in natural gas; used in the manufacture of rubber and fuels
    colorless gas found in natural gas and petroleum; used as a fuel
    a toxic mixture of gases (including carbon dioxide and carbon monoxide and nitrogen) after an explosion of firedamp in a mine
    a mixture of gases (mostly methane) that form in coal mines and become explosive when mixed with air
    a poisonous colorless flammable gas used in organic synthesis and to dope transistors and as a poison gas in warfare
    nitrogen dioxide
    a highly poisonous brown gas (NO2)
    nitric oxide
    a poisonous red-brown gas (NO)
    artificial blood
    a liquid that can carry large amounts of oxygen and can serve as a temporary substitute for blood
    blow gas, blowing gas
    the gas leaving a generator during a blow period
    butene, butylene
    any of three isomeric hydrocarbons C4H8; all used in making synthetic rubbers
    a colorless toxic gas with a pungent almond odor; has been used in chemical warfare
    exhaust, exhaust fumes, fumes
    gases ejected from an engine as waste products
    a sweet flavored liquid (usually containing a small amount of alcohol) used in compounding medicines to be taken by mouth in order to mask an unpleasant taste
    a mixture of gases (especially oxygen) required for breathing; the stuff that the wind consists of
    compressed gas
    gas at a high pressure that can be used as a propellant
    H2O, water
    binary compound that occurs at room temperature as a clear colorless odorless tasteless liquid; freezes into ice below 0 degrees centigrade and boils above 100 degrees centigrade; widely used as a solvent
    ethene, ethylene
    a flammable colorless gaseous alkene; obtained from petroleum and natural gas and used in manufacturing many other chemicals; sometimes used as an anesthetic
    an extravasated liquid (blood or lymph or urine); the product of extravasation
    air gas, producer gas
    a gas made of carbon monoxide and hydrogen and nitrogen; made by passing air over hot coke
    formaldehyde, methanal
    a colorless poisonous gas; made by the oxidation of methanol
    greenhouse emission, greenhouse gas
    a gas that contributes to the greenhouse effect by absorbing infrared radiation
    bottled gas, liquefied petroleum gas
    hydrocarbon gases, usually propane or butane, kept under pressure
    water gas
    a mixture of hydrogen and carbon monoxide with small amounts of other gases; made by blowing steam over hot coke or coal
    ideal gas, perfect gas
    a hypothetical gas with molecules of negligible size that exert no intermolecular forces
    something that is inhaled
    a liquid that is instilled drop by drop
    liquid crystal
    a liquid exhibiting properties of a crystal that are not shown by ordinary liquids
    a colorless odorless gas used as a fuel
    a colorless gas (O3) soluble in alkalis and cold water; a strong oxidizing agent; can be produced by electric discharge in oxygen or by the action of ultraviolet radiation on oxygen in the stratosphere (where it acts as a screen for ultraviolet radiation)
    a colorless poisonous gas that smells like new-mown hay; used in chemical warfare
    a colorless gas with a strong fishy smell; used as a pesticide
    poison gas
    a gas that is poisonous to breath or contact; used in chemical warfare
    propene, propylene
    a flammable gas obtained by cracking petroleum; used in organic synthesis
    a poisonous or foul smelling gas emitted from the earth
    sewer gas
    foul-smelling gas that forms in sewers
    liquid that is spilled
    the product of vaporization of a solid
    sulfur dioxide, sulphur dioxide
    a colorless toxic gas (SO2) that occurs in the gases from volcanoes; used in many manufacturing processes and present in industrial emissions; causes acid rain
    lachrymator, lacrimator, tear gas, teargas
    a gas that makes the eyes fill with tears but does not damage them; used in dispersing crowds
    a sterile liquid containing a purified protein derivative of the tuberculosis bacterium; used in the diagnosis of tuberculosis
    type of:
    that which has mass and occupies space
  2. noun
    a substance that is fluid at room temperature and pressure
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    a fluid agent (gas or liquid) that produces cooling; especially one used to cool a system by transferring heat away from one part to another
    the product of filtration; a gas or liquid that has been passed through a filter
    (Greek mythology) the rarified fluid said to flow in the veins of the Gods
    a substance that is liquid at room temperature and pressure
    beverage, drink, drinkable, potable
    any liquid suitable for drinking
    a liquid necessary for the life of most animals and plants
    the clear liquid that lies above a sediment or precipitate
    any of a series of volatile hydroxyl compounds that are made from hydrocarbons by distillation
    ammonia, ammonia water, ammonium hydroxide
    a water solution of ammonia
    a liquid added to the water in a cooling system to lower its freezing point
    distillate, distillation
    a purified liquid produced by condensation from a vapor during distilling; the product of distilling
    pyroligneous acid, wood vinegar
    a red-brown liquid formed in distillation of wood which contains acetic acid, methanol, acetone, wood oils, and tars
    a liquid with which pigment is mixed by a painter
    a liquid used for printing or writing or drawing
    a thick viscous liquid
    a liquid substance that is a solution (or emulsion or suspension) used or obtained in an industrial process
    the product of percolation
    sheep dip
    a liquid mixture containing pesticides in which sheep are dipped to kill parasites
    snake oil
    (medicine) any of various liquids sold as medicine (as by a travelling medicine show) but medically worthless
    type of:
    the real physical matter of which a person or thing consists
  3. adjective
    characteristic of a fluid; capable of flowing and easily changing shape
    synonyms: runny
    existing as or having characteristics of a liquid; especially tending to flow
  4. adjective
    subject to change; variable
    “a fluid situation fraught with uncertainty”
    synonyms: unstable
    changeable, changeful
    such that alteration is possible; having a marked tendency to change
  5. adjective
    affording change (especially in social status)
    “Britain is not a truly fluid society”
    synonyms: mobile
    changeable, changeful
    such that alteration is possible; having a marked tendency to change
  6. adjective
    smooth and unconstrained in movement
    “the fluid motion of a cat”
    synonyms: fluent, liquid, smooth
    characterized by beauty of movement, style, form, or execution
  7. adjective
    in cash or easily convertible to cash
    “liquid (or fluid) assets”
    synonyms: liquid
    free or available for use or disposition
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