A custom among industrious employees (3)
I believe the answer is:
use
'a custom' is the definition.
(I know that use is a type of custom)
'among industrious employees' is the wordplay.
'among' indicates a hidden word.
'USE' is hidden in the letters of 'industrious employees'.
(Other definitions for use that I've seen before include "particular church liturgy" , "Resort to - operation" , "Value" , "Employ or exploit" , "Employ - advantage" .)