Four involved in archly contrived gallantry (8)
I believe the answer is:
chivalry
'gallantry' is the definition.
(I know that gallantry can be written as chivalry)
'four involved in archly contrived' is the wordplay.
'four' becomes 'IV' (Roman numerals).
'involved in' means one lot of letters goes inside another.
'contrived' indicates anagramming the letters.
'archly' with letters rearranged gives 'chalry'.
'iv' inserted within 'chalry' is 'CHIVALRY'.
(Other definitions for chivalry that I've seen before include "Knightly behaviour" , "Courtesy and consideration towards women, as from knights of old" , "Medieval knightly system of honour" , "Knightly principles" , "Knightliness" .)