Tolerate assistant stealing book (5)
I believe the answer is:
abide
'tolerate' is the definition.
(synonyms)
'assistant stealing book' is the wordplay.
'assistant' becomes 'aide' (aide is a kind of assistant).
'stealing' is an insertion indicator.
'book' becomes 'b' (abbreviation for book).
'aide' placed around 'b' is 'ABIDE'.
(Other definitions for abide that I've seen before include "Bear, endure" , "live in the past?" , "Wait for" , "Put up with" , "Remain - tolerate" .)