Mediterranean is so named in winter (6)
I believe the answer is:
season
'named in winter' is the definition.
The answer and definition can be both related to time as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'mediterranean is so' is the wordplay.
I cannot quite see how this works, but
'so' could be 'as' (I've seen this in other clues) and 'as' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for season that I've seen before include "Salt, maybe" , "spring, perhaps" , "Add salt, pepper, spice etc" , "Spring, say" , "Add condiments to for time of year" .)