motiveless (adj.)

late 14c., "something brought forward, a proposition, assertion, or argument" (a sense now obsolete), from Old French motif "will, drive, motivation," noun use of adjective, literally "moving," from Medieval Latin motivus "moving, impelling," from Latin motus "a moving, motion," past participle of movere "to move" (from PIE root *meue- "to push away").

Meaning "that which inwardly moves a person to behave a certain way, mental state or force which induces an action of volition" is from early 15c. Hence "design or object one has in any action."