When you do something well, you do it in a good or satisfactory way. You can say, "I did really well on my French test," or "Finally, I slept well last night."

When well is a noun, it means "a deep hole full of water or oil." When well is an adverb, it describes the way something's done. If you're not sure when to use well and when to use good, think about what you're describing. If it's a thing, then you can call it good, like a "good book." If you're talking about an action, you should use well: "I always do well on math quizzes," or "You speak Chinese really well."

Definitions of well
  1. adverb
    (often used as a combining form) in a good or proper or satisfactory manner or to a high standard (`good' is a nonstandard dialectal variant for `well')
    “the children behaved well
    “a task well done”
    “the party went well
    “he slept well
    “a well-argued thesis”
    “a well-seasoned dish”
    “a well-planned party”
    synonyms: good
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    badly, ill, poorly
    (`ill' is often used as a combining form) in a poor or improper or unsatisfactory manner; not well
  2. adverb
    favorably; with approval
    “their neighbors spoke well of them”
    “he thought well of the book”
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    badly, ill
    unfavorably or with disapproval
  3. adverb
    with skill or in a pleasing manner
    “she dances well
    “he writes well
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    without skill or in a displeasing manner
  4. adverb
    in a manner affording benefit or advantage
    “she married well
    synonyms: advantageously
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    badly, disadvantageously
    in a disadvantageous way; to someone's disadvantage
  5. adverb
    in financial comfort
    “They live well
    synonyms: comfortably
  6. adverb
    with prudence or propriety
    “You would do well to say nothing more”
    “could not well refuse”
  7. adverb
    without unusual distress or resentment; with good humor
    “took the joke well
    “took the tragic news well
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    with unusual distress or resentment or regret or emotional display
  8. adverb
    to a great extent or degree
    “I'm afraid the film was well over budget”
    synonyms: considerably, substantially
  9. adverb
    with great or especially intimate knowledge
    “we knew them well
    synonyms: intimately
  10. adverb
    (used for emphasis or as an intensifier) entirely or fully
    “a book well worth reading”
    “was well aware of the difficulties ahead”
    “suspected only too well what might be going on”
  11. adverb
    thoroughly or completely; fully; often used as a combining form
    “The problem is well understood”
    “she was well informed”
    “shake well before using”
    “in order to avoid food poisoning be sure the meat is well cooked”
    “" well-done beef", "well-satisfied customers”
  12. adverb
    to a suitable or appropriate extent or degree
    “the project was well underway”
    “his father was well pleased with his grades”
  13. adjective
    resulting favorably
    “it is well that no one saw you”
    “all's well that ends well”
    synonyms: good
    having unexpected good fortune
  14. adjective
    in good health especially after having suffered illness or injury
    “appears to be entirely well
    “the wound is nearly well
    “a well man”
    “I think I'm well
    “at least I feel well
    physically and mentally sound or healthy
    having or indicating good health in body or mind; free from infirmity or disease
    asymptomatic, symptomless
    having no symptoms of illness or disease
    cured, healed, recovered
    freed from illness or injury
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    ill, sick
    affected by an impairment of normal physical or mental function
    not in good physical or mental condition; out of condition
    not in or exhibiting good health in body or mind
    afflicted, stricken
    grievously affected especially by disease
    affected by ague
    ailing, indisposed, peaked, poorly, seedy, sickly, under the weather, unwell
    somewhat ill or prone to illness
    air sick, airsick, carsick, seasick
    experiencing motion sickness
    characteristic of or affected with autism
    bedfast, bedrid, bedridden, sick-abed
    confined to bed (by illness)
    bilious, liverish, livery
    suffering from or suggesting a liver disorder or gastric distress
    suffering from or prone to bronchitis
    afflicted with or associated with pulmonary tuberculosis
    convalescent, recovering
    returning to health after illness or debility
    delirious, hallucinating
    experiencing delirium
    suffering from diabetes
    dizzy, giddy, vertiginous, woozy
    having or causing a whirling sensation; liable to falling
    suffering from dyspepsia
    faint, light, light-headed, lightheaded, swooning
    weak and likely to lose consciousness
    feverish, feverous
    having or affected by a fever
    experiencing odd bodily sensations
    suffering from gout
    looking pale and unhealthy
    laid low, stricken
    put out of action (by illness)
    laid up
    ill and usually confined
    affected with or related to milk sickness
    nauseated, nauseous, queasy, sick, sickish
    feeling nausea; feeling about to vomit
    affected with palsy or uncontrollable tremor
    paralytic, paralyzed
    affected with paralysis
    suffering complete paralysis of the lower half of the body usually resulting from damage to the spinal cord
    rachitic, rickety
    affected with, suffering from, or characteristic of rickets
    afflicted with scrofula
    inclined to sneeze
    suffering from spastic paralysis
    tubercular, tuberculous
    constituting or afflicted with or caused by tuberculosis or the tubercle bacillus
    not healed
    mildly physically distressed
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  15. adjective
    wise or advantageous and hence advisable
    “it would be well to start early”
    worthy of being recommended or suggested; prudent or wise
  16. adverb
    indicating high probability; in all likelihood
    “I might well do it”
    “you may well need your umbrella”
    “he could equally well be trying to deceive us”
    synonyms: easily
  17. noun
    a deep hole or shaft dug or drilled to obtain water or oil or gas or brine
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    artesian well
    a well drilled through impermeable strata into strata that receive water from a higher altitude so there is pressure to force the water to flow upward
    driven well, tube well
    a well made by driving a tube into the earth to a stratum that bears water
    gas well
    a well that yields or has yielded natural gas
    oil well, oiler
    a well that yields or has yielded oil
    a well or other hole in which water has collected
    an oil well with a strong natural flow so that pumping is not necessary
    an oil well that is spouting
    stripper, stripper well
    an oil well whose production has declined to less than ten barrels a day
    wildcat, wildcat well
    an exploratory oil well drilled in land not known to be an oil field
    type of:
    a hole in the ground made by excavating
  18. noun
    an open shaft through the floors of a building (as for a stairway)
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    a vertical well around which there is a stairway
    type of:
    a vertical passageway through a building (as for an elevator)
  19. noun
    a cavity or vessel used to contain liquid
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    inkstand, inkwell
    a small well holding writing ink into which a pen can be dipped
    type of:
    an object used as a container (especially for liquids)
  20. noun
    an enclosed compartment in a ship or plane for holding something as e.g. fish or a plane's landing gear or for protecting something as e.g. a ship's pumps
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    bilge well
    (nautical) a well where seepage drains to be pumped away
    pump well
    an enclosure in the middle of a ship's hold that protects the ship's pumps
    type of:
    a partitioned section, chamber, or separate room within a larger enclosed area
  21. noun
    an abundant source
    “she was a well of information”
    synonyms: fountainhead, wellspring
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    type of:
    a document (or organization) from which information is obtained
  22. verb
    come up, as of a liquid
    “Tears well in her eyes”
    “the currents well up”
    synonyms: swell
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    type of:
    come up, rise, rise up, surface
    come to the surface
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