Wiki says:

antagonym, Janus word (after the Roman god with two faces), enantiodrome, self-antonym, antilogy, or addad or even contranym

single words that have two opposing meanings.

just to get the list started
1) fast (speed) fast (stuck)
2) bolt (speed) bolt (fasten) - clue there for the origin of 1b)

there are many more - what are your favourite ambiguity words?