以外
いがい · igai · JLPT N4 · noun
other than
以外 = by means of (以) + outside (外): what lies outside of X
以 marks a reference point and 外 means outside, so X以外 is everything outside X, i.e. other than X. Same pattern as 以内 (within), 以上 (and above), 以下 (and below). Sound hook: igai shares gai with 外国 (gaikoku, outside country).
以 — phonetic 㠯 (plow/tool) + 人 (person)
Originally a pictograph of a hand-held plow or tool (㠯), later combined with 人 (person) to suggest 'using' something. The core meaning 'to use' extended metaphorically to 'by means of', 'with', and 'because of'. In modern Chinese it functions mainly as a grammatical particle.
外 — evening 夕 + divination 卜
Originally a compound of 夕 (evening) and 卜 (divination). Ancient Chinese divinations were performed in the morning; doing them at evening (夕) was considered irregular or 'outside' the norm. From this sense of deviation, 外 came to mean 'outside' or 'external'.