The Collaborative International Dictionary of English v.0.48:

Expansible \Ex*pan"si*ble\, a. [Cf. F. expansible.]
   Capable of being expanded or spread out widely.
   [1913 Webster]

         Bodies are not expansible in proportion to their
         weight.                                  --Grew.
   -- Ex*pan"si*ble*ness,n. -Ex*pan"si*bly,adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

expansible
    adj 1: able to expand or be expanded [syn: expandable,
           expandible, expansible]
    2: (of gases) capable of expansion [syn: expandable,
       expandible, expansible, expansile]