Sour Sour, a. [Compar. Sourer; superl. Sourest.] [OE. sour, sur, AS. s?r; akin to D. zuur, G. sauer, OHG. s?r, Icel. s?rr, Sw. sur, Dan. suur, Lith. suras salt, Russ. surovui harsh, rough. Cf. Sorrel, the plant.] 1. Having an acid or sharp, biting taste, like vinegar, and the juices of most unripe fruits; acid; tart. All sour things, as vinegar, provoke appetite. --Bacon. 2. Changed, as by keeping, so as to be acid, rancid, or musty, turned. 3. Disagreeable; unpleasant; hence; cross; crabbed; peevish; morose; as, a man of a sour temper; a sour reply. ``A sour countenance.' --Swift. He was a scholar . . . Lofty and sour to them that loved him not, But to those men that sought him sweet as summer. --Shak. 4. Afflictive; painful. ``Sour adversity.' --Shak. 5. Cold and unproductive; as, sour land; a sour marsh. Sour dock (Bot.), sorrel. Sour gourd (Bot.), the gourdlike fruit Adansonia Gregorii, and A. digitata; also, either of the trees bearing this fruit. See Adansonia. Sour grapes. See under Grape. Sour gum (Bot.) See Turelo. Sour plum (Bot.), the edible acid fruit of an Australian tree (Owenia venosa); also, the tree itself, which furnished a hard reddish wood used by wheelwrights. Syn: Acid; sharp; tart; acetous; acetose; harsh; acrimonious; crabbed; currish; peevish.