It looks like a M1917 bayonet to me, in great shape too! Depending on the handle, it could be a British P14 bayo, markings will help determine. There were subtle differences and some of the P14 bayos manufactured for Britain were issued to US troops when we entered WWI (weren't enough M1903s to go around).
The Winchester made M1917 bayos are highly collectible and rare. There are also modern counterfeits. The Remington ones are still desirable in good shape.
Great history...
http://www.usmilitaryknives.com/bayo_points_10.htm
https://en.wikipedia.org/wiki/M1917_bayonet
This bayonet will also fit trench shotguns of WWI/II.