To put one thing where another was. Replacement fills the role and is not the same thing.
Re- (Latin, again) attached to place, from Old French place, from Latin platea (a broad street), from Greek plateia (broad way); to replace is to put something into the space another thing once occupied, filling the space rather than restoring the thing.
To put one thing where another was. The root's space-filling is honest about its limits: replacement fills the role, and it is never the same thing as what it fills it with.