Summer, perhaps raining regularly over Germany in retrospect (5)
I believe the answer is:
donna
'summer' is the definition.
(musician Donna Summer)
'raining regularly over germany in retrospect' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'over' becomes 'o' (cricket abbreviation).
'germany' becomes 'd' (vehicle registration code for Deutschland).
'in retrospect' says the letters should be written in reverse (in retrospect means looking back).
The alternating letters of 'raining' are 'ann'.
'ann'+'o'+'d'='annod'
'annod' written backwards gives 'DONNA'.
'perhaps' is the link.
(Other definitions for donna that I've seen before include "Italian woman of rank" , "Title of Spanish or Portuguese lady" , "Girl" , "Spanish lady's title" , "Female" .)