Small enchantress that may light up a room (6)
I believe the answer is:
switch
'small enchantress that may light up a room' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'small enchantress' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'enchantress' becomes 'witch' (synonyms).
's'+'witch'='SWITCH'
Can you help me to learn more?
(Other definitions for switch that I've seen before include "Electrical control - change sides" , "Contact breaker; change" , "Cane to control the light" , "Exchange positions for flexible rod or whip" , "Circuit breaker; change" .)