Forty-niner, for one
I believe the answer is:
miner
'forty-niner for one' is the definition.
(forty-niner is a kind of miner)
This is all the clue.
(Other definitions for miner that I've seen before include "One tapping vein" , "Man of 49" , "Digger for gold or coal, say" , "Underground labourer" , "Excavator" .)