Thesaurus author (5)
I believe the answer is:
roget
'thesaurus author' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for roget that I've seen before include "Thesaurus maker" , "From bookmaker" , "English doctor, compiler of a thesaurus, d. 1869" , "Thesaurus constructor" , "Thesaurus creator" .)