'Unbuckle' definitions:

Definition of 'unbuckle'

From: WordNet
verb
Undo the buckle of; "Unbuckle your seat belt" [ant: buckle, clasp]

Definition of 'Unbuckle'

From: GCIDE
  • Unbuckle \Un*buc"kle\, v. t. [1st pref. un- + buckle.] To loose the buckles of; to unfasten; as, to unbuckle a shoe. "Unbuckle anon thy purse." --Chaucer. [1913 Webster]