While a string quartet is a collaborative enterprise, which musician usually takes the lead in a performance?
a. the cellist
b. the violist
c. the first violinist
d. the second violinist

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.