entries → 回信
TSUMUGU · TOCFL A2 (est.) · 詞
回信 word · TOCFL A2 (est.)
回信 ＝ 回 ＋ 信
ㄏㄨㄟˊ ㄒㄧㄣˋ · huíxìn
verb — to write back, to reply; noun — a reply letter

字源 FORM — what the parts do

回to return, back (回來)huí
信a letter (信件)xìn
回信，回來的回，信件的信。
關 · Related
回覆huífùto reply more generally — by letter or otherwise