The Collaborative International Dictionary of English v.0.48:

Curdle \Cur"dle\ (k[^u]r"d'l), v. i. [From Curd.] [Sometimes
   written crudle and cruddle.]
   1. To change into curd; to coagulate; as, rennet causes milk
      to curdle. --Thomson.
      [1913 Webster]

   2. To thicken; to congeal.
      [1913 Webster]

            Then Mary could feel her heart's blood curdle cold.
                                                  --Southey.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Curdle \Cur"dle\, v. t. [imp. & p. p. Curdled (-d'ld); p. pr.
   & vb. n. Curdling (-dl[i^]ng).]
   1. To change into curd; to cause to coagulate. "To curdle
      whites of eggs" --Boyle.
      [1913 Webster]

   2. To congeal or thicken.
      [1913 Webster]

            My chill blood is curdled in my veins. --Dryden.
      [1913 Webster]

WordNet (r) 3.0 (2006):

curdle
    v 1: turn into curds; "curdled milk" [syn: curdle, clabber,
         clot] [ant: homogenise, homogenize]
    2: go bad or sour; "The milk curdled"
    3: turn from a liquid to a solid mass; "his blood curdled"

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "curdle":
   beat up, cake, churn, clabber, clot, clump, cluster, coagulate,
   colloid, colloidize, concrete, condense, congeal, cream, curd,
   emulsify, emulsionize, ferment, gel, gelatinate, gelatinize,
   go off, incrassate, inspissate, jell, jellify, jelly, knot, lopper,
   lump, set, sour, spoil, thick, thicken, turn, whip