The Collaborative International Dictionary of English v.0.48:

Unconstrained \Unconstrained\
   See constrained.

WordNet (r) 3.0 (2006):

unconstrained
    adj 1: free from constraint; "he was unconstrained by any of the
           sanctions of polite society"; "the dog was
           unconstrained"; "idle, unconstrained gossip"

Moby Thesaurus II by Grady Ward, 1.0:

140 Moby Thesaurus words for "unconstrained":
   Bohemian, abandoned, accessible, affable, approachable, artless,
   bibulous, bluff, blunt, broad, brusque, candid, casual, common,
   communicative, conversable, cordial, crapulent, crapulous, degage,
   demonstrative, direct, downright, easy, easygoing, effusive,
   excessive, expansive, explicit, extravagant, extreme, extroverted,
   familiar, folksy, forthright, frank, frankhearted, free,
   free and easy, free-speaking, free-spoken, free-tongued, genuine,
   gluttonous, go-go, gossipy, gracious, haymish, heart-to-heart,
   homely, homey, immoderate, incontinent, indulgent, informal,
   ingenuous, inordinate, intemperate, irregular, irrepressible, lax,
   licentious, loose, low-pressure, natural, newsy, nonrestrictive,
   offhand, offhanded, open, openhearted, out of control, out of hand,
   outgoing, outspoken, overindulgent, overindulging, permissive,
   plain, plain-spoken, prodigal, rampant, reinless, relaxed, riotous,
   round, self-indulgent, self-revealing, self-revelatory, simple,
   sincere, sociable, straight, straight-out, straightforward,
   swinish, talkative, too much, transparent, unaffected, unassuming,
   unbridled, unceremonious, unchecked, uncoerced, uncompelled,
   uncontrolled, unconventional, uncurbed, undisciplined, unequivocal,
   unforced, unfrugal, unfussy, ungoverned, unguarded, unhampered,
   uninhibited, unlimited, unmastered, unmeasured, unmuzzled,
   unofficial, unreined, unrepressed, unreserved, unrestrained,
   unrestricted, unrestrictive, unreticent, unruly, unsecretive,
   unshrinking, unsilent, unstudied, unsubdued, unsuppressed,
   unthrifty, wanton, wild