The Collaborative International Dictionary of English v.0.48:

collapsible \collapsible\ adj.
   Capable of collapsing or being collapsed; as, a collapsible
   boat. [Narrower terms: telescopic; tip-up] Also See:
   folded. Antonym: noncollapsible.

   Syn: collapsable.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

collapsible
    adj 1: capable of collapsing or being collapsed; "a collapsible
           boat" [syn: collapsible, collapsable] [ant:
           noncollapsable, noncollapsible]