The Collaborative International Dictionary of English v.0.48:

Squirm \Squirm\ (skw[~e]rm), v. i. [imp. & p. p. Squirmed
   (skw[~e]rmd); p. pr. & vb. n. Squirming.] [Cf. Swarm to
   climb a tree.]
   To twist about briskly with contortions like an eel or a
   worm; to wriggle; to writhe.
   [1913 Webster]

WordNet (r) 3.0 (2006):

squirm
    n 1: the act of wiggling [syn: wiggle, wriggle, squirm]
    v 1: to move in a twisting or contorted motion, (especially when
         struggling); "The prisoner writhed in discomfort"; "The
         child tried to wriggle free from his aunt's embrace" [syn:
         writhe, wrestle, wriggle, worm, squirm, twist]

Moby Thesaurus II by Grady Ward, 1.0:

58 Moby Thesaurus words for "squirm":
   agonize, burn to, chafe, fidget, flip out, flounder, flutter,
   freak out on, fret, fuss, get excited, get high on, glow,
   go pitapat, hardly wait, hasten, have the fidgets, have the shakes,
   heave, itch to, jerk, jump the gun, palpitate, pant, quake, quaver,
   quiver, shake, shift, shiver, squiggle, stew, sweat,
   sweat and stew, sweat it out, swell, swell with emotion, thrill,
   thrill to, throb, tingle, tingle with excitement, toss,
   toss and turn, tremble, tumble, turn on to, twist, twist and turn,
   twitch, twitter, wag, waggle, wait impatiently, wiggle, worm,
   wriggle, writhe