A somewhat formal or literary term for a reply, often used in written or polite contexts. The cross-reference 返辞 is a synonym.
See also: 返事
I am waiting for his reply.
Thank you for your polite response.
Compound of 返 (へん, 'return') and 詞 (し, 'words'). The exact historical derivation is uncertain, but it follows a common pattern for forming nouns related to communication.