Too much to get on top of (4)
I believe the answer is:
over
This clue is a triple definition!
'too much' is the first definition.
(I've seen this in other clues)
'to' is the second definition.
(thesaurus)
'get' is a link.
'on top of' is the third definition.
(I've seen this in another clue)
(Other definitions for over that I've seen before include "Higher than; finished" , "Half a dozen deliveries" , "Unit of test" , "Excessive" , "Division of play in cricket" .)