Neat and chic, with varying length in a strict sense (9)
I believe the answer is:
technical
'in a strict sense' is the definition.
'neat and chic with varying length' is the wordplay.
'and' says to put letters next to each other (I've seen this in other clues).
'with varying' indicates an anagram.
'length' becomes 'l'.
'neat' put after 'chic' is 'chicneat'.
'chicneat' is an anagram of 'technica'.
'technica'+'l'='TECHNICAL'
(Other definitions for technical that I've seen before include "Relating to mechanical art or applied science" , "Requiring special knowledge to be understood" , "Requiring specialist knowledge" , "requires special skill" , "Scientific" .)