〜な
Prohibition — "don't you dare…" (入るな)machine translation
FormationVerb dictionary form + な
Placing な right after the dictionary form makes a strong prohibition: 入るな (do not enter), 触るな (don't touch). Like the imperative form, this is very forceful — used only in emergencies, on prohibition signs, or when a superior snaps at a subordinate.
Compared with 〜ないでください from N5 — the polite request "please don't…" — 〜な is a bare command with no politeness at all. In everyday communication you'll almost never say this yourself; your main job is to understand it when reading signs (ここに入るな) or hearing it in movies and stories.
Be careful not to confuse it with な attached to the ます-form with ます dropped: 食べな is the casual contraction of 食べなさい ("eat up"), the exact opposite of 食べるな ("don't eat"). Look closely at the verb form before な to tell them apart.
Examples
ここに入るな。
Do not enter here.
この川で泳ぐな。
No swimming in this river.
危ないから、触るな。
It's dangerous — don't touch it!