Stuffy sort of serials (7)
I believe the answer is:
airless
'stuffy' is the definition.
(synonyms)
'sort of serials' is the wordplay.
'sort of' is an anagram indicator.
'serials' with letters rearranged gives 'AIRLESS'.
(Other definitions for airless that I've seen before include "Stifling" , "not a breath of wind" , "Close" , "Very stuffy" , "Not ventilated" .)