サン, セン, かけはし, さ
scaffold, cleat, frame, jetty, bolt (door)
JLPT1 G7 S10 F2093
As per 戔# (fine/slight) + 木 tree/wood → (object made of) fine pieces of wood → *jetty*; *frame* (of a sliding door); *fence* (← constructions made of small pieces of wood joined together).
[Full Kanji Etymology List]