Word books somehow suit her admirably at first (8)
I believe the answer is:
thesauri
'word books' is the definition.
(I've seen this in another clue)
'somehow suit her admirably at first' is the wordplay.
'somehow' indicates anagramming the letters.
'at first' indicates taking the first letters.
The first letter of 'admirably' is 'a'.
'suit'+'her'+'a'='suithera'
'suithera' anagrammed gives 'THESAURI'.
(Other definitions for thesauri that I've seen before include "Reference works providing synonyms" , "reference books" , "Word books" , "Dictionaries" , "they may aid writers" .)