Unusually large top, bought initially for Juliet (6)

I believe the answer is:

bumper

I'm a little stuck... Click here to teach me more about this clue!

'unusually large' is the definition.
(I've seen this before)

I don't understand the rest of the clue.

(Other definitions for bumper that I've seen before include "generous amount of alcohol" , "kind of car" , "jumbo" , "Protective vehicle bar" , "Unusually large" .)

I've seen this clue in The Telegraph.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.