回首
huí shoǔ · HSK 7
to look back
🔙 回 (return/turn back) + 首 (head) = turn the head back, i.e. look back
回 means to return or turn back; 首 means head. Together they literally mean turning the head back, which extends from a physical glance behind you to recollecting the past.
回 — enclosure 囗 + smaller 囗 inside
回 is a pictograph of a swirling whirlpool or coiled spiral, shown as nested squares in modern form. The original meaning was 'to revolve' or 'turn around,' which extended to 'return' and 'a time/occurrence.' It also appears as a phonetic in characters like 茴 and 廻.
首 — hair 丷 over face 自 (eye + nose)
首 is a pictograph of a head, originally drawn with hair on top and a face below (containing the eye element 目). It meant 'head' literally, then extended to 'chief, leader, first' since the head is the topmost and foremost part of the body.