Source : Webster's Revised Unabridged Dictionary (1913)

Unaccustomed \Un`ac*cus"tomed\, a.
   1. Not used; not habituated; unfamiliar; unused; -- which to.

            Chastened as a bullock unaccustomed to yoke. --Jer.
                                                  xxxi. 18.

   2. Not usual; uncommon; strange; new.

            What unaccustomed cause procures her hither? --Shak.

Source : WordNet®

unaccustomed
     adj 1: not habituated to; unfamiliar with; "unaccustomed to wearing
            suits" [ant: {accustomed}]
     2: not customary or usual; "an unaccustomed pleasure"; "many
        varieties of unaccustomed foods"; "a new budget of
        unaccustomed austerity"