Contronyms
'Sanction' can approve or punish
One sense comes from making something holy and lawful, the other from enforcing that law. Context alone tells you which.
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'Cleave' means both to split and to cling
A contronym is its own opposite. Cleave descends from two different Old English verbs that collided into one modern spelling.
'Dust' can add or remove
You dust a cake with sugar and dust a shelf to remove dust. The verb faces both directions.
'Oversight' watches and misses
Oversight means careful supervision and also a careless mistake, two meanings that sit uncomfortably close in law.