Somewhat assiduous pair of people (3)
I believe the answer is:
duo
'pair of people' is the definition.
'somewhat assiduous' is the wordplay.
'somewhat' indicates the answer is hidden within the clue.
'DUO' can be found hidden inside 'assiduous'.
(Other definitions for duo that I've seen before include "Couple, pair" , "entertainers such as Eric and Ernie" , "Pair of singers" , "Two players" , "Item" .)