Square root of 49 (5)
I believe the answer is:
seven
'square root of 49' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for seven that I've seen before include "Wonders of the World - Deadly Sins" , "Number of colours of the rainbow" , "Figure of dwarfs?" , "Number of Wonders of the World" , "Number of sins, seas or dwarves" .)