TSUMUGU · TOCFL B1 (est.) · 字
姻
ㄧㄣ · yīn
noun — marriage, a marriage tie (chiefly the wife's side, in-laws)
字源 FORM — what the parts do
因 yīn does double work here: it lends the sound and the sense both. 因 is a person lying on a mat — what one relies on, the basis; and a marriage is exactly the tie a woman (女) comes to rely on, the bond between two families: 婚姻、姻緣、姻親.
故事 STORY — a scene to remember it by
一個女子（女）出嫁，從此多了一層所依（因）的人家。
A woman (女) marries out, and from then on there is a household she leans on (因).
字源記憶法
意 · Meanings
(本義)婚姻— marriage常用
→姻緣、姻親— a marriage bond; in-laws常用
(本義) original meaning · → ⇒ each arrow = one more step of extension