The adjective variable is used to describe something that is liable to change often, such as the weather, interest rates, or your teacher's mood.

If you mention the noun variable to people who are math-phobic, you may give them nightmares because they don't like to think about numbers or values that can change in equations. The adjective form of variable has been around since the late 1300s, applying first to people, and then, in the late 1400s, to weather. The noun form first appeared in Lacroix's Differential and Integral Calculus in 1816, guaranteeing that math students would be solving for the variable x for generations to come.

Definitions of variable
  1. noun
    something that is likely to vary; something that is subject to variation
    “the weather is one variable to be considered”
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    type of:
    a separate and self-contained entity
  2. noun
    a quantity that can assume any of a set of values
    synonyms: variable quantity
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    a variable in a logical or mathematical expression whose value determines the dependent variable; if f(x)=y, x is the independent variable
    experimental variable, independent variable
    (statistics) a variable whose values are independent of changes in the values of other variables
    correlate, correlative
    either of two or more related or complementary variables
    degree of freedom
    (statistics) an unrestricted variable in a frequency distribution
    dependent variable
    (statistics) a variable in a logical or mathematical expression whose value depends on the independent variable
    predictor variable
    a variable that can be used to predict the value of another variable (as in statistical regression)
    (mathematics) a variable that has zero as its limit
    chance variable, random variable, stochastic variable, variant, variate
    a variable quantity that is random
    a variable quantity that cannot be resolved into components
    a generalization of the concept of a vector
    a variable quantity that can be resolved into components
    an independent variable in statistics
    cross product, vector product
    a vector that is the product of two other vectors
    resultant, vector sum
    a vector that is the sum of two or more other vectors
    radius vector
    a line connecting a point in space to the origin of a polar coordinate system
    radius vector
    a line connecting a satellite to the center of the body around which it is rotating
    type of:
    the concept that something has a magnitude and can be represented in mathematical expressions by a constant or a variable
  3. noun
    a symbol (like x or y) that is used in mathematical or logical expressions to represent a variable quantity
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    a symbol in a logical or mathematical expression that can be replaced by the name of any member of specified set
    unknown, unknown quantity
    a variable whose values are solutions of an equation
    type of:
    an arbitrary sign (written or printed) that has acquired a conventional significance
  4. noun
    a star that varies noticeably in brightness
    synonyms: variable star
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    North Star
    the brightest star in Ursa Minor; at the end of the handle of the Little Dipper; the northern axis of the earth points toward it
    type of:
    (astronomy) a celestial body of hot gases that radiates energy derived from thermonuclear reactions in the interior
  5. adjective
    marked by diversity or difference
    “nature is infinitely variable
    synonyms: varying
    characterized by variety
  6. adjective
    liable to or capable of change
    “rainfall in the tropics is notoriously variable
    variable winds”
    variable expenses”
    displaying a lack of consistency
    likely to change frequently often without apparent or cogent reason; variable
    changeable, uncertain, unsettled
    subject to change
    changing so that interrelations with another variable quantity or set of quantities remain unchanged
    pertaining to any procedure involving two or more variables
    taking on different forms
    continuously varying
    exhibiting variation and change
    changeable or inconstant
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    not liable to or capable of change
    (sometimes followed by `with') in agreement or consistent or reliable
    steadfast in purpose or devotion or affection
    changeless, constant, invariant, unvarying
    unvarying in nature
    hard-and-fast, strict
    (of rules) stringently enforced
    unaffected by a designated operation or transformation
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  7. adjective
    (used of a device) designed so that a property (as e.g. light) can be varied
    “a variable capacitor”
    variable filters in front of the mercury xenon lights”
    capable of adapting (of becoming or being made suitable) to a particular situation or use
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