1590s, "liable to make answer or defense, accountable," from Anglo-French amenable, from Old French amener "bring, take, conduct, lead" (to the law), from "to" (see ad-) + mener "to lead," from Latin minare "to drive (cattle) with shouts," variant of minari "to threaten," also "to jut, project" (from PIE root *men- (2) "to project"). Sense of "tractable" is from 1803, from notion of "disposed to answer or submit to influence." Related: Amenably.
The spelling with a- is unusual but early and also is found in Provençal and Italian. In English it has been supplanted in senses of "repair; cure" by its shortened offspring mend (v.). Meaning "to add to legislation" (ostensibly to correct or improve it) is recorded from 1777. Related: Amended; amending.