Surge? This does, regularly (4)
I believe the answer is:
'surge?' is the definition.
(I know that surge can be written as tide)
'this does regularly' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternating letters of 'thisdoes' are 'TIDE'.
(Other definitions for tide that I've seen before include "Season; current" , "Powerful surge" , "What might carry" , "Current, ebb" , "One thing that waits for no man" .)