カン, せき, ぜき, かか.わる, からくり, かんぬき
connection, barrier, gateway, involve, concerning
JLPT3 G4 S14 F70
The lower element# is as per 丱 (two boards pierced by a connecting rod) + 幺 slender thread (doubled) → connect two objects by piercing each and inserting thread or cord through holes in them (compare 串 and 穿). 關 adds 門 gate → *shut* a gate by connecting its two doors with a *bolt* or *bar* → *connect*; *barrier*; *checkpoint*. Also, *be involved* (← have a connection with).
[Full Kanji Etymology List]