Grammar › N4 · 11 Particles and endings, more
な: don't!; isn't it...
N4 · 11 Particles and endings, more
Dictionary form + な means a negative command; also a casual feeling.
Verb dictionary form + な = prohibition (rough). Plain form + な = musing, 'it's a ...' (masculine). Not the な of na-adjectives.
Examples
危ないから触るな。
It's dangerous, so don't touch it.
今日は本当にいい天気だな。
It's really nice weather today.