Source : Webster's Revised Unabridged Dictionary (1913)

Usable \Us"a*ble\, a.
   Capable of being used.

Source : WordNet®

usable
     adj 1: able to be put to use; "usable byproducts" [syn: {useable}]
     2: fit or ready for use or service; "the toaster was still
        functional even after being dropped"; "the lawnmower is a
        bit rusty but still usable"; "an operational aircraft";
        "the dishwasher is now in working order" [syn: {functional},
         {useable}, {in working order(p)}, {operable}, {operational}]
     3: convenient for use or disposal; "the house is available
        after July 1"; "2000 square feet of usable office space"
        [syn: {available}, {useable}]