They hold a hundred lights (6)
I believe the answer is:
clamps
'they hold a' is the definition.
The definition suggests an adverb but the answer is not.
'hundred lights' is the wordplay.
'hundred' becomes 'c' (Roman numeral).
'lights' becomes 'lamps' (lamp is a kind of light).
'c'+'lamps'='CLAMPS'
Can you help me to learn more?
(Other definitions for clamps that I've seen before include "Grips" , "fasteners" , "Devices to hold things, car wheels say" , "Device to hold things, car wheels say" , "Holds tightly with device - illegally parked cars? (6)" .)