A licit form of character (6)
I believe the answer is:
italic
'character' is the definition.
(italic is a kind of character)
'a licit form' is the wordplay.
'form' indicates anagramming the letters (another form of the letters).
'a'+'licit'='alicit'
'alicit' with letters rearranged gives 'ITALIC'.
'of' is the link.
(Other definitions for italic that I've seen before include "Type of script" , "from Rome?" , "identifies a branch of languages?" , "Type used for stress" , "Slanting character" .)