Pester constantly (3)
I believe the answer is:
nag
'pester constantly' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nag that I've seen before include "Termagant" , "(Of pain) ache dully; horse (colloq.)" , "Jade" , "its head to name the pub" , "Annoy constantly" .)