Feeble books covered by attack (6)
I believe the answer is:
flabby
'feeble' is the definition.
(thesaurus)
'books covered by attack' is the wordplay.
'books' becomes 'bb' (two abbreviations for book).
'covered by' is an insertion indicator.
'attack' becomes 'flay' (flay can mean to criticise or attack).
'bb' going within 'flay' is 'FLABBY'.
(Other definitions for flabby that I've seen before include "Saggy" , "Relating to loose, hanging fat" , "Flaccid" , "More than ample" , "Slack, loose (skin)" .)