Highest roll of a single die (3)
I believe the answer is:
six
'highest roll of a single die' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for six that I've seen before include "Airborne boundary hit" , "Half a dozen" , "Number of bowls in a cricket over" , "Knock for . . . - surprise or defeat" , "VI" .)