Specialised food shop, one third of it (4)

I believe the answer is:

deli

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

'specialised food shop' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for deli that I've seen before include "part of supermarket" , "Fine-food store" , "Unusual food shop" , "Food shop or counter" , "food outlet" .)

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.