Citrus fruit found in Jerusalem once (5)
I believe the answer is:
lemon
'citrus fruit' is the definition.
(I know that lemon is a type of citrus fruit)
'in jerusalem once' is the wordplay.
'in' says the answer is hidden in the clue.
'LEMON' can be found hidden inside 'jerusalem once'.
'found' acts as a link.
(Other definitions for lemon that I've seen before include "Tone" , "Fruit squeezed on Pancake Day?" , "Shade of yellow - fruit" , "Unhelpful answer" , "Fruit (which is proverbially "the answer")" .)