Singer standing, having registered cloud (11)
I believe the answer is:
altostratus
'cloud' is the definition.
(I know that altostratus is a type of stratus)
'singer standing having registered' is the wordplay.
'singer' becomes 'alto' (type of singing voice).
'standing' becomes 'status' (I've seen this in another clue).
'having' is an insertion indicator.
'registered' becomes 'R' (abbreviation, as in registered trademark).
'status' enclosing 'r' is 'stratus'.
'alto'+'stratus'='ALTOSTRATUS'
(Other definitions for altostratus that I've seen before include "Sky feature" , "Cloud forming a uniform layer" .)