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