Heavy book about anger, small and boring (8)
I believe the answer is:
tiresome
'boring' is the definition.
('tiresome' can be a synonym of 'boring')
'heavy book about anger small' is the wordplay.
'heavy book' becomes 'tome' (I've seen this before).
'about' is an insertion indicator.
'anger' becomes 'ire' ('ire' can be a synonym of 'anger').
'small' becomes 's' (abbreviation - e.g. clothes size).
'ire'+'s'='ires'
'tome' placed around 'ires' is 'TIRESOME'.
'and' acts as a link.
(Other definitions for tiresome that I've seen before include "irritating" , "wearing" , "Annoying, being a nuisance" , "Like a pain" , "Boring, irksome (colloq.)" .)