Small pasty-faced bulb developer (4)
I believe the answer is:
swan
'bulb developer' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'small pasty-faced' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'pasty-faced' becomes 'wan' (I've seen this in another clue).
's'+'wan'='SWAN'
Can you help me to learn more?
(Other definitions for swan that I've seen before include "... Australian river" , "Mute, whooper or Bewick's bird" , "Cob - pen" , "Whooper or trumpeter?" , "Large aquatic bird" .)