Wind in low cloud slowing, mostly (7)
I believe the answer is:
mistral
'wind' is the definition.
(mistral is a kind of wind)
'low cloud slowing mostly' is the wordplay.
I cannot quite see how this works, but
'cloud' could be 'mist' (synonyms) and 'mist' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'in' acts as a link.
Can you help me to learn more?
(Other definitions for mistral that I've seen before include "Strong wind down the 20 valley" , "Violent northeast wind of southern France" , "Nice chiller" , "That's a blow" , "French wind" .)