Is it farther or further?
c.1300, "intention, aim, goal," from Anglo-French purpos, Old French porpos "aim, intention" (12c.), from porposer "to put forth," from por- "forth" (from Latin pro- "forth;" see pur-) + Old French poser "to put, place" (see pose (v.1)). On purpose "by design" is attested from 1580s; earlier of purpose (early 15c.).
late 14c., from Anglo-French purposer "to design," Old French porposer "to intend, propose," variant of proposer (see propose).