不 + Adjective
不 (bù) is a negation adverb meaning "not." When placed before an adjective, it negates that quality, creating the opposite meaning. For example, 不相同 means "not the same."
这个方案不合理,需要修改。
Zhège fāng'àn bù hélǐ, xūyào xiūgǎi.
This plan is unreasonable and needs to be revised.
今天不冷,穿件薄外套就够了。
Jīntiān bù lěng, chuān jiàn báo wàitào jiù gòu le.
It's not cold today; a thin jacket is enough.
这两个词的意思不一样。
Zhè liǎng gè cí de yìsi bù yīyàng.
These two words have different meanings.