noun
Specifically the wooden frame or stile of a sliding door (障子や襖の框).
障子の桟が外れてしまった。
The frame of the sliding screen came off.
noun
A horizontal or transverse bar used in construction, furniture, or joinery.
この椅子の桟が折れてしまった。
The crosspiece of this chair broke.
noun
sliding wooden bolt (for a door or window)
A traditional wooden latch that slides horizontally to secure a door or window; also called 猿 (さる) in some contexts.
See also: 猿
雨戸の桟をかけて鍵をかける。
Slide the wooden bolt on the storm shutter to lock it.
框 is a broader term for a door or window frame, while 桟 often refers to a thinner crosspiece or a sliding bolt.
猿 (sense 4) is a synonym for the sliding wooden bolt, but 桟 is the more common term in architectural contexts.
The kanji 桟 is composed of 木 (tree, wood) and 戔 (a phonetic element suggesting 'small' or 'narrow'), indicating a narrow wooden piece. The exact historical derivation is uncertain.