Cloud begins receding, claims university (7)
I believe the answer is:
stratus
'cloud' is the definition.
(stratus cloud is a kind of cloud)
'begins receding claims university' is the wordplay.
'begins' becomes 'starts' ('start' can be a synonym of 'begin'**).
'receding' shows that the letters should be reversed in order.
'claims' indicates putting letters inside.
'university' becomes 'u'.
'starts' back-to-front is 'strats'.
'strats' going around 'u' is 'STRATUS'.
(Other definitions for stratus that I've seen before include "Source of rain" , "Sheet of low cloud" , "Grey cover" , "Could carry rain" , "Cloud as a grey sheet" .)