Nimbus, say (5)
I believe the answer is:
cloud
'nimbus say' is the definition.
(nimbus is a kind of cloud)
This is the entire clue.
(Other definitions for cloud that I've seen before include "''I wandered lonely as a ...'' (Wordsworth)" , "Make less clear" , "Obscure" , "Dull spot" , "It hides the sun" .)