Contranyms are single words that have two contradictory meanings (they are their own opposites!). They are somewhat rare. Still, here are 10 of them:
1. Apology: a statement of contrition (sorrow) for an act, or a firm defense of one
2. Bolt: to secure, or to flee
3. Bound: heading to a destination, running off ('bounding away') OR restrained from movement at all
4. Cleave: to adhere to, or to separate
5. Dust: to add fine particles, or to removed them
6. Fast: quick, or stuck/made stable
7. Left: remained, or departed
8. Peer: a person of the nobility, or an equal (actually the 2nd came out of the first; the peers were each other's equals, with rights the hoi polloi didn't have)
9. Sanction: to approve, or to boycott
10. Weather: to withstand, to wear away
