Fruit yours truly left at work (5)
I believe the answer is:
melon
'fruit' is the definition.
(I know that melon is a type of fruit)
'yours truly left at work' is the wordplay.
'yours truly' becomes 'me' (the person that set this crossword).
'left' becomes 'l' (common abbreviation).
'at work' becomes 'on' (on can mean activated or working).
'me'+'l'+'on'='MELON'
(Other definitions for melon that I've seen before include "Edible gourd" , "Eg, cantaloupe, galia" , "Type of pepo" , "Sweet juicy gourd" , "Honeydew fruit" .)