I needed to use the word “sanction” the other day and thought about how it has two opposite meanings (a contronym): A sanction means approving of something (asking a boss to sanction your project) or sanctioning by boycotting (as in sanctioning certain companies that take positions you do not agree with).
The word “cleave” is similarly a contronym, meaning to stick to something (The toddler cleaved to her mother’s arm) and also to split or sever (Pioneers needed to cleave logs to keep their cabins warm).
Here are some more contronyms on a list from this source: http://blog.oxforddictionaries.com/2012/06/contronyms/
dust: 1 to remove dust. 2 to cover with dust.
hysterical: 1 frightened and out of control. 2 funny.
nervy: 1 showing nerve or courage. 2 excitable and volatile.
moot: 1 debatable. 2 not worth debating. (Pronounced as spelled, not as MUTE)
fast: 1 moving quickly. 2 solid and unable to move.
seed: 1 to sow seeds. 2 to remove seeds.
weather: 1 to withstand a storm. 2 to wear away.
screen: 1 to show, e.g., a film. 2 to hide something.
bound: 1 fastened to a spot. 2 heading for somewhere.
apology: 1 an expression of regret for something. 2 a defense or justification of something.
strike: 1 to hit. 2 to miss (in baseball).
I love being a word nerd.