Number of deadly sins (5)
I believe the answer is:
seven
'number of deadly sins' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for seven that I've seen before include "Dwarfs or Wonders of the World?" , "So many ages of man (AYLI)" , "Film" , "Number of colours of the rainbow" , "Number of seas sailed?" .)