The Collaborative International Dictionary of English v.0.48:

make believe \make" be*lieve`\, v. i.
   To pretend; -- often used with that, but often having the
   that omitted; as, he made believe he didn't hear her; or he
   made believe that he didn't hear her.
   [PJC]

WordNet (r) 3.0 (2006):

make believe
    v 1: represent fictitiously, as in a play, or pretend to be or
         act like; "She makes like an actress" [syn: make,
         pretend, make believe]

Moby Thesaurus II by Grady Ward, 1.0:

128 Moby Thesaurus words for "make believe":
   act, act a part, affect, affected, apocryphal, apparition,
   artificial, assume, assumed, bastard, bluff, bogus, brainchild,
   brummagem, bubble, charade, chimera, colorable, colored,
   counterfeit, counterfeited, cover up, delirium, disguise,
   dissemble, dissimulate, distorted, dressed up, dummy, eidolon,
   embellished, embroidered, ersatz, fabulous, factitious, fake,
   faked, falsified, fancy, fantasque, fantasy, feign, feigned,
   fiction, fictional, fictitious, fictive, figment, figmental,
   four-flush, gammon, garbled, hallucination, idle fancy,
   illegitimate, illusion, imagery, imagination, imagining, imitation,
   insubstantial image, invention, junky, legendary, let on,
   let on like, maggot, make a pretense, make as if, make like,
   man-made, mock, myth, mythic, mythicized, mythified, mythological,
   nonactual, nonfactual, nonrealistic, pageant, perverted, phantasm,
   phantom, phony, pinchbeck, play, play a part, play possum, playact,
   pretend, pretended, pretension, pretentiousness, profess, pseudo,
   put on, put-on, quasi, queer, romance, self-styled, sham, shoddy,
   sick fancy, simulate, simulated, so-called, soi-disant, spurious,
   supposititious, synthetic, thick-coming fancies, tin, tinsel,
   titivated, trip, twisted, unauthentic, ungenuine, unnatural,
   unreal, vapor, vision, warped, whim, whimsy, wildest dreams