不意
ふい · fui · JLPT N1 · na-adj
sudden
⚡ 不 (not) + 意 (expectation): not expected, so sudden or unexpected
不 means not and 意 means intention or expectation, so 不意 is what was not expected. It appears as 不意に (fui ni), meaning suddenly, and 不意打ち means a surprise attack.
不 — single pictograph; bird flying upward
Originally a pictograph in oracle bone script, traditionally interpreted as a bird flying up toward the sky and unable to come down, suggesting negation or refusal. Over time it became the standard negation word in Chinese, used before verbs and adjectives to mean 'not'.