Fit or ready for use or service. Synonyms:functional, operable, operational, useable."The lawnmower is a bit rusty but still usable" , "An operational aircraft" , "The dishwasher is now in working order"
Convenient for use or disposal. Synonyms:available, useable."2000 square feet of usable office space"
... even of mammals, which comprises the most perfect animals, and chiefly those in which the vertebrate plan of organization is most perfectly carried out, not only the baleen has no usable teeth, but the ant-eater (Myrmecophaga) is also in the same condition, whose habit of not masticating its food has been for a long time established and ... — Lamarck, the Founder of Evolution - His Life and Work • Alpheus Spring Packard