The same three-letter word has been removed from each of the following clues. Can you determine what it is?

1.     _ _ _ IO
2. C _ _ _ ER
3. W _ _ _ H
4. I _ _ _ E

HINT:
MIG _ _ _ E

Answer:

The missing word is RAT:

1.  RATIO
2.  CRATER
3.  WRATH
4.  IRATE
     (MIGRATE)