One shot better than the colonel (3)
I believe the answer is:
par
'one' is the definition.
The answer and definition can be both quantities as well as being singular nouns.
Maybe there's a link between them I don't understand?
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for par that I've seen before include "normal amount" , "Average standard" , "Mean" , "Face value; equal standing" , "level footing" .)