thin

Concise Oxford English Dictionary © 2008 Oxford University Press:
thin/θɪn/

▶adjective (thinner, thinnest)

• 1 having opposite surfaces or sides relatively close together.

  ■ (of a garment or similar item) made of light material.

  ■ (of a garment or fabric) having become less thick as a result of wear.

• 2 having little flesh or fat on the body.

• 3 having few parts or members relative to the area covered or filled; sparse.

  ■ not dense or heavy: the thin air of the mountains.

• 4 containing much liquid and not much solid substance.

• 5 (of a sound) faint and high-pitched.

  ■ (of a smile) weak and forced.

• 6 lacking substance or quality; inadequate or weak: the evidence is rather thin.

▶adverb with little thickness. ▶verb (thins, thinning, thinned)

• 1 make or become less thick.

• 2 remove some plants from (a row or area) to allow the others more room to grow.

• 3 Golf hit (a ball) above its centre.

– phrases
be thin on the ground see ground1.
have a thin time Brit. informal have a miserable or uncomfortable time.
thin air used to refer to the state of being invisible or non-existent.
the thin blue line informal the police.

– derivatives
thinly adverb,
thinness noun,
thinnish adjective.

– origin OE thynne, of Gmc origin.