不然 bùrán
不然（bùrán）means “不然: 'otherwise / or else'”. 不然 (bùrán) means 'otherwise, or else'. Formation: …，不然(就)…（否则，不这样的话）
不然: 'otherwise / or else'
HSK4Formation
…，不然(就)…（否则，不这样的话）
Explanation
不然 (bùrán) means 'otherwise, or else'. It stands at the head of the second clause: do X, 不然 (if not) a bad consequence follows. It equals 要不然/否则 but is more colloquial than 否则.
Examples
快点走，不然就迟到了。
kuài diǎn zǒu, bùrán jiù chídào le.
Hurry up, or else we'll be late.
多穿点，不然会感冒。
duō chuān diǎn, bùrán huì gǎnmào.
Wear more, otherwise you'll catch a cold.
Note
Colloquial; also 要不然. Followed by the consequence of not acting.
FAQ
不然 — what does it mean and how is it used?
不然: 'otherwise / or else'. 不然 (bùrán) means 'otherwise, or else'. It stands at the head of the second clause: do X, 不然 (if not) a bad consequence follows. It equals 要不然/否则 but is more colloquial than 否则.
不然 — how do you form it?
…，不然(就)…（否则，不这样的话）
不然 — any usage notes?
Colloquial; also 要不然. Followed by the consequence of not acting.