late 14c., "to help, support, maintain," also "fill up, make up for," from Old French supplier "fill up, make full," from Latin supplere "fill up, complete," from sub "up from below" + plere "to fill" (see pleio-). The meaning "furnish, provide" first recorded 1520s. Related: Supplied; supplying.
early 15c., "assistance, relief," from supply (v.). Meaning "quantity or amount of something provided" is attested from c.1600. In the political economy sense (corollary of demand) it dates from 1776. Supply-side in reference to economic policy is attested from 1976. Supplies "provisions" is from c.1650.
The amount of any given commodity available for sale at a given time.