Number of suspects in Clue (3)
I believe the answer is:
six
'number of suspects in clue' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for six that I've seen before include "Number of bowls in a cricket over" , "Knock for . . . - surprise or defeat" , "Half-dozen" , "larger boundary" , "Half a dozen" .)