What is "tiebeam"

Tiebeam \Tie"beam`\, n. (Arch.) A beam acting as a tie, as at the bottom of a pair of principal rafters, to prevent them from thrusting out the wall. See Illust. of Timbers, under Roof.
--Gwilt.

n. (context architecture English) A beam acting as a tie, as at the bottom of a pair of principal rafters, to prevent them from thrusting out the wall.