Difficult book about Russian money (11)
'difficult' is the definition.
(similar in meaning)
'book about russian money' is the wordplay.
'book' becomes 'tome' (a tome is a book).
'about' indicates putting letters inside.
'russian money' becomes 'roubles' (I've seen this before).
'tome' going around 'roubles' is 'TROUBLESOME'.
(Other definitions for troublesome that I've seen before include "Causing annoyance", "Mischievous - vexatious", "likely to cause ructions", "Trying", "problematic".)