Autoantonyms are words with two directly opposite meanings. For example, 'sanction' is an autoantonym, because it can mean "to support" or "to condemn".
Another word in this category is 'left': it can mean "departed" ('The man left') or it can mean "stayed" ('There's only one man left'). In fact, this can give rise to potentially ambiguous utterances with two directly contradictory meanings. For example:
There's only one man who's left.
which could mean one man departed or one man stayed behind. This is because 's' could be the weak form of 'has' or of 'is'.
Interestingly, this confusion is unlikely to occur in somewhere like Brunei, in which the weak worm of 'has' almost never occurs. Sometimes avoiding weak forms can help in maintaining intelligibility and avoiding misunderstandings.
