Cumulonimbus initially thunderous: what is it? (5)
I believe the answer is:
cloud
'is it?' is the definition.
I can't tell whether this definition defines the answer.
'cumulonimbus initially thunderous' is the wordplay.
'initially' suggests taking the first letters.
'thunderous' becomes 'loud' (similar in meaning).
The initial letter of 'cumulonimbus' is 'c'.
'c'+'loud'='CLOUD'
'what' acts as a link.
Can you help me to learn more?
(Other definitions for cloud that I've seen before include "It hides the sun" , "Visible vapour in sky" , "Make less transparent" , "Cumulus, for example" , "Visible mass floating above" .)