Writer hides a saint in the restaurant (6)
I believe the answer is:
bistro
'the restaurant' is the definition.
(bistro is a kind of restaurant)
'writer hides a saint' is the wordplay.
'writer' becomes 'biro' (type of pen, something which writes).
'hides' is an insertion indicator.
'a saint' becomes 'st' (abbreviation).
'biro' enclosing 'st' is 'BISTRO'.
'in' acts as a link.
(Other definitions for bistro that I've seen before include "Modest restaurant" , "Cafe bar" , "Small informal French restaurant" , "Intimate eatery" , "'Small, inexpensive restaurant (6)'" .)