It's forbidden; and badly one hundred take it (7)
I believe the answer is:
illicit
'it's forbidden' is the definition.
(I've seen this in another clue)
'badly one hundred take it' is the wordplay.
'badly' becomes 'i'll' ('ill' can be adverbial as in 'ill-advised').
'one' becomes 'i' (Roman numeral).
'hundred' becomes 'c' (Roman numeral).
'take' is a charade indicator (letters next to each other).
'ill'+'i'+'c'+'it'='ILLICIT'
'and' acts as a link.
(Other definitions for illicit that I've seen before include "Not allowed, unlawful" , "Not legal" , "Under the counter" , "Prohibited" , "Unacceptable" .)