needn't

Etymology
.

Verb

 * 1)  Need not.
 * 2) * 1926 July, D[avid] H[erbert Richards] Lawrence, “”, , New York, N.Y.:, 1639362 :
 * ‘Oh no,’ said the boy casually. ‘I won’t think much about them, mother. You needn’t worry. I wouldn’t worry, mother, if I were you.’ / ‘If you were me and I were you’, said his mother, ‘I wonder what we should do!’ / ‘But you know you needn’t worry, mother, don’t you?’ the boy repeated.
 * ‘Oh no,’ said the boy casually. ‘I won’t think much about them, mother. You needn’t worry. I wouldn’t worry, mother, if I were you.’ / ‘If you were me and I were you’, said his mother, ‘I wonder what we should do!’ / ‘But you know you needn’t worry, mother, don’t you?’ the boy repeated.

Usage notes

 * Needn’t is not synonymous with mustn’t, except in questions. “Needn’t you do it?” and “Mustn’t you do it?” both mean “Don’t you have to do it?”, but “You mustn’t do it.” means you must avoid doing it and “You needn’t do it.” means you do not have to do it but presumably still may, though it can imply that doing so is pointless.
 * The auxiliary need, like the auxiliary dare, can only be used intransitively. “I don’t need to have it.” can be swapped with “I needn’t have it.” but “I don’t need it.” cannot be swapped with “I needn’t it.”, since that would require taking a direct object, whereas “I need it not.” would work, though unidiomatic.