early 15c., "to enlarge, expand, increase," from Old French amplifier (15c.), from Latin amplificare "to enlarge," from amplus "large" (see ample) + combining form of facere "to make, do" (from PIE root *dhe- "to set, put"). Meaning "augment in volume or amount" is from 1570s. Restriction of use to sound seems to have emerged from c. 1915 in reference to radio technology.
