Also found in: Thesaurus, Medical, Encyclopedia, Wikipedia.


Contraction of must not.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


contraction of
must not
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014


(ˈmʌs ənt)
contraction of must not.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.


(mast) negative short form ˈmustn't (-snt) verb
1. used with another verb to express need. We must go to the shops to get milk.
2. used, usually with another verb, to suggest a probability. They must be finding it very difficult to live in such a small house.
3. used, usually with another verb, to express duty, an order, rule etc. You must come home before midnight; All competitors must be under 15 years of age.
something necessary, essential, or not to be missed. This new tent is a must for the serious camper.
must have
used to state a probability about something in the past. She must have been very young when she got married.
Kernerman English Multilingual Dictionary © 2006-2013 K Dictionaries Ltd.
References in classic literature ?
Oh, I'm so sorry; but you mustn't, really, ever get scared about me, Nancy.
But you mustn't fancy,' cried the gentleman, quite elated by coming so happily to his point.
"You mustn't do that," said he; "they won't have anything ready.
"You mustn't talk like that," she protested, "you with your splendid courage and opportunities!
Rook say something of my father which I mustn't hear?"
Tom grasped his hand, and continued,--"Ye mustn't, now, tell Chloe, poor soul!
Now mind, Muster Gashford,' said the fellow, taking up his stick and shaking it with a ferocious air, 'I mustn't have my Protestant work touched, nor this here Protestant state of things altered in no degree, if I can help it; I mustn't have no Papists interfering with me, unless they come to be worked off in course of law; I mustn't have no biling, no roasting, no frying--nothing but hanging.
She screamed out all at once "You mustn't speak like this of Papa!"
you mustn't! you mustn't," exclaimed Edna, and pushing back her chair she got up, and going behind him placed her hand over his mouth.
It swore every boy to stick to the band, and never tell any of the secrets; and if anybody done anything to any boy in the band, whichever boy was ordered to kill that person and his family must do it, and he mustn't eat and he mustn't sleep till he had killed them and hacked a cross in their breasts, which was the sign of the band.
"I look like a drudge," said Rebecca mysteriously, with laughing eyes, "but I really am a princess; you mustn't tell, but this is only a disguise; I wear it for reasons of state.
"Oftens and oftens," said Bruno, "haven't oo told me ' There mustn't be so much noise, Bruno!' when I've tolded oo 'There must!' Why, there isn't no rules at all about 'There mustn't'!