Small sun lamp (6)
I believe the answer is:
slight
'small' is the definition.
(thesaurus)
'sun lamp' is the wordplay.
'sun' becomes 's'.
'lamp' becomes 'light' (I've seen this before).
's'+'light'='SLIGHT'
(Other definitions for slight that I've seen before include "Slim or tenuous" , "Insignificant, flimsy" , "Insubstantial; discourtesy" , "Deliberate rebuff" , "Insubstantial; insult" .)