From The Collaborative International Dictionary of English v.0.48 :
Usable \Us"a*ble\, a. Capable of being used. [1913 Webster]From WordNet (r) 3.0 (2006) :
usable adj 1: capable of being put to use; "usable byproducts" [syn: useable, usable] 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, usable, useable, operable, operational] 3: convenient for use or disposal; "the house is available after July 1"; "2000 square feet of usable office space" [syn: available, usable, useable]