Lickspittle (6)
'lickspittle' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for sycophant that I've seen before include "Austen's Mr Collins?" , "obsequious one" , "receiving ultimate in flattery from one such?" , "Creep" , "Uriah Heep, say" .)
(Another definition for yesman that I've seen is " A most agreeable chap".)