thin / [unvoicedth]in/ • adj. (thin·ner, thin·nest) 1. having opposite surfaces or sides close together; of little thickness or depth: thin slices of bread. ∎  (of a person) having little, or too little, flesh or fat on their body: she was painfully thin. ∎  (of a garment or other knitted or woven item) made of light material for coolness or elegance. ∎  (of a garment) having had a considerable amount of fabric worn away. ∎  (of script or type) consisting of narrow lines: tall, thin lettering.2. having few parts or members relative to the area covered or filled; sparse: a depressingly thin crowd his hair was going thin. ∎  not dense: the thin cold air of the mountains. ∎  containing much liquid and not much solid substance: thin soup. ∎ Climbing denoting a route on which the holds are small or scarce.3. (of a sound) faint and high-pitched: a thin, reedy little voice. ∎  (of a smile) weak and forced. ∎  too weak to justify a result or effect; inadequate: the evidence is rather thin.• adv. [often in comb.] with little thickness or depth: thin-sliced ham cut it as thin as possible.• v. (thinned, thin·ning) 1. make or become less dense, crowded, or numerous: [tr.] the remorseless fire of archers thinned their ranks | [intr.] the trees began to thin out | [as adj.] (thinning) thinning hair. ∎  [tr.] remove some plants from (a row or area) to allow the others more room to grow: thin out overwintered rows of peas. ∎  make or become weaker or more watery: [tr.] if the soup is too thick, add a little water to thin it down | [intr.] the blood thins. 2. make or become smaller in width or thickness: [tr.] their effect in thinning the ozone layer is probably slowing the global warming trend | [intr.] the trees have thinned and diminished in size. 3. [tr.] Golf hit (a ball) above its center.PHRASES: on thin icesee ice.thin air used to refer to the state of being invisible or nonexistent: she just vanished into thin air they seemed to pluck numbers out of thin air.the thin blue line inf. used to refer to the police, typically in the context of situations of civil unrest.thin end of the wedgesee wedge.thin on top inf. balding.DERIVATIVES: thin·ly adv.thin·ness n. thin·nish adj.ORIGIN: Old English thynne, of Germanic origin; related to Dutch dun and German dünn, from an Indo-European root shared by Latin tenuis.

thin into thin air used to refer to the state of being invisible or non-existent.
the thin red line the British army (in reference to the traditional scarlet uniform); the phrase first occurs in the war correspondent William Howard Russell's book The British Expedition to the Crimea (1877) of the Russians charging the British at Balaclava. Russell's original dispatch to The Times, 14 November 1854, had read ‘That thin red streak topped with a line of steel’. In an alteration of the phrase, the police are sometimes referred to as the thin blue line.

See also thin as Banbury cheese, on thin ice, as thin as a rake.

thin OE. þynne = OS. thunni (Du. dun), OHG. dunni (G. dünn), ON. þunnr :- Gmc. *þunnuz (:- *þunw-), based on IE. *tṇ, zero-grade of *ten- *ton- draw out, stretch (repr. also in Lat. tenuis thin, etc.).

thin In a cultivated crop, to remove some plants in order to increase the area available to others. In forestry, to remove some of the trees in an area to enable those that remain to grow larger, especially in girth.

thin In a cultivated crop, to remove some plants in order to increase the area available to others. In forestry, to remove some of the trees in an area to enable those that remain to grow larger, especially in girth.