ONE-UPMANSHIP
Credit: NY Times Crossword - Oct. 22, 1989
Phyllis Fehringer -Idea - (adapted)

Most adjectives ending in Y form their comparative form by changing the Y to I and adding ER - as in HEAVY and HEAVIER. All the words in the list below follow this rule, yet two of them are different from the others. Can you determine which words are different and why?

HEAVY
RAINY
SHADY
FUNNY
TANGY
ROOMY
SILLY

HINT;
The two words which are different are RAINY and TANGY.

Answer:

RAINIER and TANGIER are heteronyms. 
Mount Ranier is a mountain in Washington. 
Tangier is a Moroccan seaport.