Many a light grip (5)
I believe the answer is:
clamp
'grip' is the definition.
(thesaurus)
'many a light' is the wordplay.
'many' becomes 'c' (C is the Roman numeral for l00).
'a light' becomes 'lamp' (lamp is a kind of light**).
'c'+'lamp'='CLAMP'
(Other definitions for clamp that I've seen before include "Wheel immobiliser" , "stack of bricks" , "bracket" , "Grip firmly" , "Secure - store for potatoes" .)