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):

curdling
    n 1: the process of forming semisolid lumps in a liquid [syn:
         curdling, clotting, coagulation]