The Collaborative International Dictionary of English v.0.48:

Unofficial \Unofficial\
   See official.

WordNet (r) 3.0 (2006):

unofficial
    adj 1: not having official authority or sanction; "a sort of
           unofficial mayor"; "an unofficial estimate"; "he
           participated in an unofficial capacity" [ant: official]
    2: not officially established; "the early election returns are
       unofficial"

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "unofficial":
   Bohemian, actionable, affable, against the law, anarchic,
   anarchistic, anomic, apocryphal, black-market, bootleg, casual,
   chargeable, contraband, contrary to law, cordial, criminal, degage,
   easy, easygoing, familiar, felonious, flawed, folksy,
   free and easy, gracious, haymish, homely, homey, illegal,
   illegitimate, illicit, impermissible, informal, irregular,
   justiciable, lawless, loose, natural, nonconstitutional, nonlegal,
   nonlicit, nonofficial, offhand, offhanded, outlaw, outlawed, plain,
   punishable, relaxed, simple, sociable, triable, unaffected,
   unallowed, unassuming, unattested, unauthentic, unauthenticated,
   unauthoritative, unauthorized, unceremonious, uncertified,
   unchecked, unconfirmed, unconstitutional, unconstrained,
   unconventional, uncorroborated, undemonstrated, under-the-counter,
   under-the-table, unlawful, unproved, unstatutory, unstudied,
   unvalidated, unverified, unwarrantable, unwarranted, wrongful