Caret's key (3)
I believe the answer is:
six
'caret's key' 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 "VI" , "Knock for . . . - surprise or defeat" , "Half a dozen" , "Number of bowls in a cricket over" , "Number of US moon landings" .)