means To respond to a message, question, or statement, especially in speech or writing.

from From Old French 'replier,' to fold back or turn back, which came from Latin 'replicare' — 're-' (back) plus 'plicare' (to fold), the same 'fold' that lives in 'plait,' 'pleat,' and 'complicated.' So a reply is, quite literally, the conversation folding back on itself — your words bent back toward the sender. The same Latin root later gave English 'replica' and 'replicate,' those other things that fold and double the original.