The Collaborative International Dictionary of English v.0.48:

Unceremonious \Unceremonious\
   See ceremonious.

WordNet (r) 3.0 (2006):

unceremonious
    adj 1: without ceremony or formality; "an unceremonious speech"
           [syn: unceremonious, unceremonial]
    2: without due formalities; "unceremonious dismissal from
       office"

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "unceremonious":
   Bohemian, affable, casual, cordial, degage, easy, easygoing,
   familiar, folksy, free and easy, gracious, haymish, homely, homey,
   inconsiderate, informal, irregular, loose, natural, offhand,
   offhanded, plain, relaxed, sharp, simple, sociable, thoughtless,
   unaffected, unassuming, unconstrained, unconventional, ungracious,
   unofficial, unstudied