Like controversial verses thus written about a function (7)
I believe the answer is:
satanic
'like controversial verses' is the definition.
(as in Salman Rushdie's novel The Satanic Verses)
'thus written about a function' is the wordplay.
'thus' becomes 'sic' ('thus' in Latin).
'written about' means one lot of letters goes inside another.
'function' becomes 'tan' (tangent, mathematical function).
'a'+'tan'='atan'
'sic' going around 'atan' is 'SATANIC'.
(Other definitions for satanic that I've seen before include "Like the Devil" , "Nick's" , "Demonic" , "Relating to the devil" , "Devilish (as Blake's 18)" .)