A multitude some author described (5)
I believe the answer is:
horde
'a multitude' is the definition.
(I know that horde is a type of multitude)
'some author described' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'HORDE' is hidden in the letters of 'author described'.
(Other definitions for horde that I've seen before include "Migratory tribe; army" , "Great crowd" , "Nomadic army" , "Large group of people" , "A moving crowd" .)