The bulb possibly lit up (5)
I believe the answer is:
tulip
'the bulb' is the definition.
(I've seen this before)
'possibly lit up' is the wordplay.
'possibly' indicates anagramming the letters.
'lit'+'up'='litup'
'litup' with letters rearranged gives 'TULIP'.
(Other definitions for tulip that I've seen before include "Amsterdam bloom?" , "Plant of the lily family with a single showy flower" , "Bulbous plant" , "Liliaceous plant with a spring flower" , "It blooms in 11 down" .)