Insurance for a hundred and more (5)
I believe the answer is:
cover
'insurance' is the definition.
(I've seen this before)
'hundred and more' is the wordplay.
'hundred' becomes 'c' (Roman numeral).
'and' says to put letters next to each other.
'more' becomes 'over' (I've seen this before).
'c'+'over'='COVER'
'for a' is the link.
(Other definitions for cover that I've seen before include "Lid, travel (distance)" , "Disguise" , "Encompass" , "Fielder" , "(Put) lid (on) - fielding position - insurance" .)