Fruit revealed by lifting nail gun (4)
I believe the answer is:
ugli
'fruit' is the definition.
(ugli fruit is a kind of fruit)
'revealed by lifting nail gun' is the wordplay.
'lifting' says the letters should be written backwards.
'revealed by' indicates a hidden word.
'ilgu' is hidden within 'nail gun'.
'ilgu' in reverse letter order is 'UGLI'.
(Other definitions for ugli that I've seen before include "Grapefruit/tangerine hybrid" , "Orange-grapefruit cross" , "mixed fruit" , "Trademark name for a hybrid citrus fruit" , "Tropical fruit" .)