WordNet (r) 3.0 (2006):

catch on
    v 1: understand, usually after some initial difficulty; "She
         didn't know what her classmates were plotting but finally
         caught on" [syn: catch on, get wise, get onto,
         tumble, latch on, cotton on, twig, get it]
    2: become popular; "This fashion caught on in Paris"

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "catch on":
   absorb, appreciate, apprehend, ascertain, assimilate, be blooded,
   be hep to, be on to, be successful, be wise to, be with one,
   become popular, become the rage, catch, catch on to, click,
   come off, comprehend, conceive, connect, determine, dig, digest,
   farewell, fathom, find out, follow, get, get hold of,
   get the drift, get the idea, get the picture, go, go great guns,
   go off, go over, go over big, go to town, graduate, grasp, have,
   have it taped, hear, ken, know, learn, make a hit, master,
   meet with success, pass, penetrate, prevail, prosper, qualify,
   read, realize, savvy, see, see through, seize, seize the meaning,
   sense, succeed, take, take in, tumble, tumble to, understand,
   unearth, wise up to, work well, work wonders