Definitions

1. verb

to require or demand something

“She needn’t worry about the deadline, as it’s been extended.”

2. auxiliary verb

used to form the negative of a verb or to express necessity or obligation

“You needn’t come in today, the office is closed.”

3. auxiliary verb (informal)

used to express necessity or obligation in informal contexts

“You needn’t be there, but it would be nice if you were.”