The Collaborative International Dictionary of English v.0.48:

Freak \Freak\, v. i.
   1. to react with irrationality or extreme emotion; to lose
      one's composure; -- often used in the phrase

   freak out.
      [PJC]

   2. to become irrational or to experience hallucinations under
      the influence of drugs; -- often used in the phrase

   freak out.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Freak \Freak\, v. t.
   1. to cause (a person) react with great distress or extreme
      emotion; -- often used in the phrase

   freak out.
      [PJC]

WordNet (r) 3.0 (2006):

freak out
    n 1: a wild delusion (especially one induced by a hallucinogenic
         drug) [syn: disorientation, freak out]
    v 1: lose one's nerve; "When he saw the accident, he freaked
         out" [syn: freak out, freak, gross out]

Moby Thesaurus II by Grady Ward, 1.0:

96 Moby Thesaurus words for "freak out":
   adore, appreciate, bask in, be pleased with, becharm, bewitch,
   captivate, carry away, charm, daydream, delectate, delight,
   delight in, derive pleasure from, devour, dream, dream of, eat up,
   enchant, enjoy, enrapture, enravish, enthrall, entrance, fantasy,
   fascinate, feast on, fidget, flip out, flutter, freak out on,
   get high on, gloat over, glow, go ape, go bananas, go crackers,
   go pitapat, groove on, hallucinate, have the fidgets,
   have the shakes, heave, imparadise, indulge in, jerk, knock dead,
   knock out, like, love, luxuriate in, palpitate, pant, pipe-dream,
   quake, quaver, quiver, ravish, rejoice in, relish, revel in,
   riot in, savor, send, shake, shiver, slay, smack the lips, squirm,
   swell, swell with emotion, swim in, take pleasure in, thrill,
   thrill to, throb, tickle, tickle pink, tingle,
   tingle with excitement, titillate, toss, toss and turn, transport,
   tremble, trip, tumble, turn on to, twist and turn, twitch, twitter,
   wallow in, wiggle, wow, wriggle, writhe