Ha! You've been reading Bill Bryson's Mother Tongue!
I'd call them contronyms.

Here are some more:-

sanguine (bloodthirsty or calm and cheerful)
ravish (to rape or to enrapture)
trying (doing one's best or being annoying)
blunt (dull as used for an instrument, but to the point when used for a remark)
They're quite useful when writing school reports. For example, "James has been trying this term."