Final “y” before a suffix

When a word ends in y preceded by a consonant, the y usually changes to i when adding a suffix:

• curly —> curlier
• party —> parties
• thirty —> thirties, thirtieth

However, if the suffix begins with i, the y does not change (except before the suffix ize):

• thirty —> thirtyish
• fry —> frying
• agony —> agonize
• memory —> memorize

When a final y is preceded by a vowel, it does not change to i:

• journey —> journeying
• trolley —> trolleys