Light onion, for example (4)
I believe the answer is:
bulb
I believe this is a double definition.
'light' is the first definition.
(bulb is a kind of light)
'onion for example' is the second definition.
(onion is a kind of bulb)
(Other definitions for bulb that I've seen before include "A tulip grows from one" , "Tulip, for example" , "From which a tulip or light comes" , "This provides light" , "Eg, hyacinth" .)