1. a volatile liquid, as turpentine, used to dilute paint, varnish, rubber cement, etc., to the desired or proper consistency.
  2. a person who adds thinners to paints, varnishes, etc.
  3. a person who specializes in weeding plants, pruning shrubbery, thinning fruit, etc.


  1. comparative of thin.

adjective, thin·ner, thin·nest.

  1. having relatively little extent from one surface or side to the opposite; not thick: thin ice.
  2. of small cross section in comparison with the length; slender: a thin wire.
  3. having little flesh; spare; lean: a thin man.
  4. composed of or containing objects, particles, etc., widely separated; sparse: thin vegetation.
  5. scant; not abundant or plentiful.
  6. of relatively slight consistency or viscosity: thin soup.
  7. rarefied, as air.
  8. without solidity or substance; flimsy: a very thin plot for such a long book.
  9. lacking fullness or volume; weak and shrill: a thin voice.
  10. without force or a sincere effort: a thin smile.
  11. lacking body, richness, or strength: a thin wine.
  12. lacking in chroma; of light tint.
  13. Photography. (of a developed negative) lacking in density or contrast through underdevelopment or underexposure.


  1. in a thin manner.
  2. sparsely; not densely.
  3. so as to produce something thin: Slice the ham thin.

verb (used with object), thinned, thin·ning.

  1. to make thin or thinner (often followed by down, out, etc.).

verb (used without object), thinned, thin·ning.

  1. to become thin or thinner; become reduced or diminished (often followed by down, out, off, etc.): The crowd is thinning out.


  1. (often plural, functioning as singular) a solvent, such as turpentine, added to paint or varnish to dilute it, reduce its opacity or viscosity, or increase its penetration into the ground

adjective thinner or thinnest

  1. of relatively small extent from one side or surface to the other; fine or narrow
  2. slim or lean
  3. sparsely placed; meagrethin hair
  4. of relatively low density or viscositya thin liquid
  5. weak; poor; insufficienta thin disguise
  6. (of a photographic negative) having low density, usually insufficient to produce a satisfactory positive
  7. mountaineering a climb or pitch on which the holds are few and small
  8. thin on the ground few in number; scarce


  1. in order to produce something thinto cut bread thin

verb thins, thinning or thinned

  1. to make or become thin or sparse

n.liquid used to dilute paint, ink, etc., 1904, agent noun from thin (v.). adj.Old English þynne “narrow, lean, scanty,” from Proto-Germanic *thunnuz, *thunw- (cf. West Frisian ten, Middle Low German dunne, Dutch dun, Old High German dunni, German dünn, Old Norse þunnr), from PIE *tnus-, *tnwi-, from weak grade of root *ten- “stretch” (cf. Latin tenuis “thin, slender;” see tenet). These our actors … were all Spirits, and Are melted into Ayre, into thin Ayre. [Shakespeare, “The Tempest,” IV.i.150, 1610] Thin-skinned is attested from 1590s; the figurative sense of “touchy” is from 1670s. v.Old English þynnian “to make thin” (cf. German dünnen, Dutch dunnen), from thin (adj.). Intransitive sense of “to become less numerous” is attested from 1743; that of “to become thinner” is recorded from 1804. Related: Thinned; thinning. In addition to the idioms beginning with thin

  • thin as a rail
  • thin edge of the wedge
  • thing or two
  • things are looking up
  • thin on top
  • also see:

  • into thin air
  • on thin ice
  • spread oneself too thin
  • through thick and thin
  • wear thin
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