Contronyms
'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.
More in 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.
'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.