Replace comes from French replacer — 're- + placer' — meaning 'to place again'. The root traces through Latin platea ('broad street') to Greek platys ('broad, flat'), which also gives us plaza, plateau, and platypus.
To take the place of something or someone; to put something back in its original position; to provide a substitute.
From Old French replacer, from re- 'back, again' + placer 'to place, to put', from place meaning 'an open space, a broad street', from Medieval Latin placea, from Latin platea meaning 'broad street, open area', from Greek plateia (hodos) meaning 'broad (street)', from platys meaning 'broad, flat'. Replace is a relatively late addition to English — it did not appear until the 1590s. Before it arrived, English used restore, renew, or put back. The word's structure is transparent: to place again, to put back. Key
Replace, plaza, plateau, platform, plate, and platypus all trace back to Greek platys meaning 'broad, flat'. A plaza is a broad open space. A plateau is a broad flat highland. A platform is a flat form. A plate is a flat dish. And a platypus has broad, flat feet (platys + pous, 'flat-footed'). Replace puts something back in its broad, flat place.