Source : Webster's Revised Unabridged Dictionary (1913)

Penetrable \Pen"e*tra*ble\, a. [L. penetrabilus: cf. F.
   p['e]n['e]trable.]
   Capable of being penetrated, entered, or pierced. Used also
   figuratively.

         And pierce his only penetrable part.     --Dryden.

         I am not made of stones, But penetrable to your kind
         entreats.                                --Shak.
   -- {Pen"e*tra*ble*ness}, n. -- {Pen"e*tra*bly}, adv.

Source : WordNet®

penetrable
     adj 1: admitting of penetration or passage into or through; "a
            penetrable wall"; "penetrable defenses" [ant: {impenetrable}]
     2: capable of being penetrated; "penetrable defenses"