Mingle with grockles, initially, in pool (5)
I believe the answer is:
merge
'mingle' is the definition.
(thesaurus)
'grockles initially in pool' is the wordplay.
'initially' says to take the initial letters.
'in' is an insertion indicator.
'pool' becomes 'mere' (mere is a kind of pool).
The initial letter of 'grockles' is 'g'.
'g' inserted within 'mere' is 'MERGE'.
'with' is the link.
(Other definitions for merge that I've seen before include "Come together as one" , "Become combined" , "Combine elements" , "Combine, blend" , "Combine, coalesce" .)