The Collaborative International Dictionary of English v.0.48:

Jell \Jell\, v. i.
   1. To jelly. [Colloq.]
      [1913 Webster]

   2. To take on a more concrete or substantial form; -- of
      ideas, plans, programs, etc.
      [PJC]

WordNet (r) 3.0 (2006):

jell
    v 1: become gelatinous; "the liquid jelled after we added the
         enzyme" [syn: jell, set, congeal]

Moby Thesaurus II by Grady Ward, 1.0:

81 Moby Thesaurus words for "jell":
   albumen, batter, beat up, bonnyclabber, butter, cake, churn,
   clabber, clot, clump, cluster, coagulate, cohere, colloid,
   colloidize, come together, concrete, congeal, cornstarch, cream,
   crystallize, curd, curdle, dough, egg white, emulsify, emulsionize,
   gaum, gel, gelatin, gelatinate, gelatinize, glair, glop, glue,
   gluten, goo, gook, goop, gruel, gumbo, gunk, harden, incrassate,
   inspissate, jam, jellify, jelly, knot, loblolly, lopper, lump,
   materialize, molasses, mucilage, mucus, pap, paste, porridge,
   pudding, pulp, puree, putty, rob, semifluid, semiliquid, set, size,
   solidify, soup, starch, stick, sticky mess, stiffen, syrup,
   take form, take shape, thick, thicken, treacle, whip