除非
chúfēi · HSK 5
unless
除非 = remove (除) + not (非); 'unless you remove the not'
除 means to remove/divide; 非 means not/non-. Together they form a conditional: the only case left after removing all 'not' cases — i.e., 'only if' or 'unless'.
除 — left ear/mound 阝 + surplus 余
除 combines the 'mound/steps' radical 阝 (originally 阜, a hill) with 余 as the phonetic. It first meant the steps of a palace, then extended to 'remove' or 'clear away' (as one sweeps steps clean), and later to mathematical 'divide.'
非 — two opposing wings 羽-like form
Originally a pictograph showing two wings spread in opposite directions, symbolizing things facing away from each other. From this 'opposition' image came the meaning 'not' or 'wrong.' It is also used as a phonetic component in many characters like 排, 悲, and 罪.