From three +‎ point +‎ -er.

three-pointer (plural three-pointers)

1. (sports) A goal or other means of scoring worth three points.
   • 1944, “Football at mid-season”, in Columbia Alumni News:

     Here Colgate stiffened, so Will place-kicked a 33-yard three-pointer from the 23 to put the Lions in front 10-7.

   • 1982, David Parry-Jones, The Golden Years of Welsh Rugby:

     Barry John's try was the last three-pointer to be scored for Wales.

2. (basketball) A three-point shot; a basket made from beyond the three-point line.
   • 1948, The Official National Collegiate Athletic Association Basketball Guide:

     A basket by Texas' Hamilton and a three-pointer by Madsen put the Longhorns ahead.

   • 1966, Bob Pettit, Bob Wolf, Bob Pettit: The Drive Inside Me:

     I'd like to see a long shot beyond an established line become a three pointer. It would stand out like a home run in baseball.

3. (aviation) A three-point landing; an airplane landing in which all three wheels touch the ground simultaneously.
   • October 1930, Paul Paddock, "I Solo in Seven Hours", Popular Mechanics

     Away I roared once more, resolved to score a three-pointer. I glided down to a good start but estimated my altitude wrongly.

4. (hunting) A deer or other animal whose antlers feature three points or tines.
   • 1918, John B. Griffin, “A Fight with the 'Bald Faced' Bear”, in Oregon Sportsman:

     ...one a three-pointer, the other a seven-pointer, and the one still lying down, a spike.