Iam a word that begins with the letter i. if you add the letter a to me, i become a new word with a different meaning, but that sounds exactly the same. what word am i?

your word would be isle.

isle is an island or peninsula especially a small one.

if you add the letter "a" you get aisle, which is a passage between 2 rows of something like chairs, shelves, or something else.

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