mustn't
Prohibited from doing
Mustn't is the contraction of must not, expressing prohibition or strong advice against something: You mustn't tell anyone.
It carries more force than shouldn't—closer to forbidden than inadvisable.
More common in British than American English, where must not or can't often substitute.
Lacking the ability
- won'tContraction showing refusal
- shouldn'tAdvised against doing
- couldn'tPast inability marker
- wouldn'tPast conditional negative
shan't · needn't · oughtn't · hasn't · haven't · hadn't · isn't · aren't
Not allowed
- prohibitedOfficially not permitted
- disallowedOfficially not permitted
- bannedOfficially disallowed
- off-limitsProhibited from access
taboo · restricted · impermissible · not allowed · out of bounds · verboten · unauthorized · illicit
Required moral task
- requirementMandatory condition to fulfill
- imperativeUnavoidably necessary
- necessityIndispensable requirement
- mandateFormal authoritative directive
compulsion · rule · stipulation · precondition · prerequisite · expectation · commandment · directive
can't
Lacking the ability
wouldn't · shan't · needn't · oughtn't · hasn't · haven't · hadn't · isn't · aren't · wasn't
forbidden
Not allowed
- prohibitedOfficially not permitted
- disallowedOfficially not permitted
- bannedOfficially disallowed
off-limits · taboo · restricted · impermissible · not allowed · out of bounds · verboten · unauthorized · illicit · barred
duty
Required moral task
- requirementMandatory condition to fulfill
- imperativeUnavoidably necessary
- necessityIndispensable requirement
mandate · compulsion · rule · stipulation · precondition · prerequisite · expectation · commandment · directive · injunction
beware
Exercise vigilant caution
careful · watch out · warning · risk · hazard · peril · threat · alarm · red flag · heads up