不然
bùrán · HSK 4
otherwise
不 = not + 然 = so; 'not so' → otherwise / if not
不 means 'not' and 然 means 'so/like that' (as in 当然 'of course'). Together 不然 literally reads 'not so,' which extends to 'otherwise' or 'if not [the case].' Use it to introduce an alternative or warn of a consequence.
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'.