Insure for a lot too much (5)
I believe the answer is:
cover
'insure' is the definition.
(synonyms)
'lot too much' is the wordplay.
'lot' becomes 'c' ().
'too much' becomes 'over' (over can mean to too great an extent).
'c'+'over'='COVER'
'for a' acts as a link.
(Other definitions for cover that I've seen before include "Mask, hide" , "the point of cricket" , "Deal with" , "Lid, travel (distance)" , "Extend over (an area)" .)