A licit special typeface (6)
I believe the answer is:
italic
'typeface' is the definition.
(I know that italic is a type of typeface)
'a licit special' is the wordplay.
'special' indicates an anagram.
'a'+'licit'='alicit'
'alicit' anagrammed gives 'ITALIC'.
(Other definitions for italic that I've seen before include "Letters written sloping to the right" , "Sloping type of print" , "Slanting character" , "(Of text) sloping" , "Printed in a sloping type" .)