An answer sent back to whoever asked. A reply closes a turn and opens the next.
Old French replier, from Latin replicare (to fold back): re- (back) + plicare (to fold); a reply is, at its root, a folding-back of an answer toward whoever first spoke.
An answer sent back to whoever asked. The root's folding-back closes one turn of a conversation and, by the same motion, opens the next.