haud

Haud is an emphatic negative, and the difference from non is one of scope. Non usually negates the whole sentence; haud fastens onto a single word and denies it hard. That word is normally an adjective, an adverb or a pronoun: haud facile, haud multum, haud ignotus, haud secus. English "by no means" is often the closest fit.

With verbs it is rare, and in classical prose it is effectively restricted to scio. That gives the fixed haud scio an, twin of nescio an, which despite appearances is a POSITIVE statement: "I rather think, I am inclined to believe", not "I do not know whether". Anybody who translates it literally will make Cicero sound indecisive when he is being tactful.

Haud never negates a command. Latin uses ne with the subjunctive or with noli for that, and using haud there is not merely unidiomatic, it is not Latin.