Other forms: replied, replies, replying
To reply is to answer, to say or write something back to someone who spoke or wrote to you first. A reply to an email, a wave back across the street, "fine, thanks" when a neighbour asks how you are.
It is the noun as well: a reply, three replies, no reply at all. The word takes TO, so you reply to a letter, to a question, to a message, and never "reply a letter". Reply sits a step above answer in tone, which is why software puts Reply and Reply All on the buttons and why an old business letter opens with "in reply to yours of 5 March". It stretches beyond words too, as when an army replies to shelling or a team replies with a goal of its own. Watch the spelling when it changes shape: he replies, he replied, she is replying.
1verbreplyTo say or write something back to someone.
“She replied within an hour to say the room was still free.”
synonyms: respond, answer
2nounwordsThe words said or written back to someone; an answer.
“I sent three messages and got no reply.”
3verbactionTo answer an action with a matching one.
“The home side replied with two goals in five minutes.”
Also accepted in games: respond
It came through Old French replier from Latin replico, to fold back, built from re-, back, and plico, to fold. A reply was once a folding of the paper back the way it came. The same Latin verb gives English replica and replicate, so a reply and a copy are cousins.
Proto-Indo-European
*pleḱ-
Latin
replico — to fold back
Old French
replier — to reply
Middle English
replyen
English, today
reply
Built from
From Middle English replyen, replien, borrowed from Old French replier (“to reply”), from the Latin replico (“to fold back”) (in Late or Medieval Latin "to reply, repeat"), from re + plicō (“to fold”); the noun derives from the verb by nominalisation. Doublet of replicate and replica.
Etymology from Wiktionary, CC BY-SA