Characteristic of cap set askew (6)
I believe the answer is:
aspect
'characteristic' is the definition.
(aspect is a kind of characteristic)
'cap set askew' is the wordplay.
'askew' indicates anagramming the letters.
'cap'+'set'='capset'
'capset' with letters rearranged gives 'ASPECT'.
'of' acts as a link.
(Other definitions for aspect that I've seen before include "The appearance presented" , "Viewpoint, feature to be considered" , "Characteristic to be considered" , "Particular part or feature of something" , "View or facet" .)