mid-15c., "supplementary payment, amount needed to complete repayment," from Late Latin implementem "a filling up" (as with provisions), from Latin implere "to fill, fill up, make full; fatten; fulfill, satisfy," from assimilated form of in- "into, in, on, upon" (from PIE root *en "in") + plere "to fill" (from PIE root *pele- (1) "to fill"). Sense of "workman's tool, utensil of a trade, things necessary to do work" is 1530s. The underlying connection of the senses is "whatever may supply a want, that which fills up a need." Related: Implemental; implements.
"to complete, perform, carry into effect," 1707, originally chiefly in Scottish English, where the noun was a legal term meaning "fulfillment," from implement (n.). It spawned implementation, which is first recorded 1913. Related: Implemented; implementing.