Thin  —adj. (thinner, thinnest) 1 having opposite surfaces close together; of small thickness or diameter. 2 (of a line) narrow or fine. 3 made of thin material (thin dress). 4 lean; not plump. 5 not dense or copious (thin hair). 6 of slight consistency. 7 weak; lacking an important ingredient (thin blood; a thin voice). 8 (of an excuse etc.) Flimsy or transparent. —adv. Thinly (cut the bread very thin). —v. (-nn-) 1 (often foll. By down) make or become thin or thinner. 2 (often foll. By out) make or become less dense or crowded or numerous.  have a thin time colloq. Have a wretched or uncomfortable time. Thin on the ground few in number. Thin on top balding.  thinly adv. Thinness n. Thinnish adj. [old english]