A grossly misused reference (8)
I believe the answer is:
glossary
'reference' is the definition.
(I know that glossary is a type of wordbook)
'a grossly misused' is the wordplay.
'misused' indicates anagramming the letters.
'a'+'grossly'='agrossly'
'agrossly' anagrammed gives 'GLOSSARY'.
(Other definitions for glossary that I've seen before include "where terms are laid out" , "A grossly distorted kind of word list" , "Alphabetical list of technical terms" , "Specialised dictionary" , "Index of terms" .)