Passionate about (4)
'passionate about' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for into that I've seen before include "digging" , "Involved with" , "To a position inside" , "To a position within" , "A fan of" .)
(Other definitions for mad that I've seen before include "Angry or insane" , "like the March Hare" , "Frenzied" , "Frantic" , "(Of a dog) rabid" .)
'passionate about' is the definition.
(I've seen this in another clue)
This is all the clue.