What's it called when you have two words that are spelled the same but have opposite meanings?

Question

Example: resign

To quit or 

Re-sign as in to sign a new contract. 

Answer 1

It's not called "when."

What's the term for a word which has opposite meanings?  A contronym.

Answer 2

Contronym. Two word that sound the same, but have different and opposite  meanings.

Sanction: to give permission

Sanction: to hold responsible for misdeed. 

Auto--antonym, is also correct.

Source(s): Native American English speaker for 68 years

Answer 3

Auto-Antonym....

Answer 4

Contronym.     

Answer 5

UNKNOWN..UNKNOWN

Answer 6

Homonyms