Source : Webster's Revised Unabridged Dictionary (1913)

Extensible \Ex*ten"si*ble\, a. [Cf. F. extensible. See
   {Extend}.]
   Capable of being extended, whether in length or breadth;
   susceptible of enlargement; extensible; extendible; -- the
   opposite of contractible or compressible. ``An extensible
   membrane'' --Holder.

Source : WordNet®

extensible
     adj : capable of being protruded or stretched or opened out; "an
           extensile tongue"; "an extensible measuring rule" [syn:
            {extensile}] [ant: {nonextensile}]

Source : Free On-Line Dictionary of Computing

extensible
     
         Said of a system (e.g., {program}, {file
        format}, {programming language}, {protocol}, etc.) designed to
        easily allow the addition of new {features} at a later date,
        e.g. through the use of {hooks}, an {API} or {plug-ins}.
     
        See also {extend}, {forward compatible}.
     
        (1998-01-15)