Extract from author describing multitude (5)
I believe the answer is:
horde
'multitude' is the definition.
(I know that horde is a type of multitude)
'extract from author describing' is the wordplay.
'extract from' says the answer is hidden in the clue (some letters extracted from the clue).
'HORDE' can be found hidden inside 'author describing'.
(Other definitions for horde that I've seen before include "Large crowd" , "Large army" , "Huge noisy crowd" , "lots of people" , "Great crowd" .)