I. ˈ ̷ ̷| ̷ ̷ adjective
Etymology: Middle English thre sqware having three equal sides, from three, thre three + sqware, square square
: having an equilateral triangular cross section — used especially of a file
II. ˈ ̷ ̷ˌ ̷ ̷ noun
1. also three-square rush
[so called from the triangular stems]
: any of various rushes of the genus Scirpus ; especially : chairmaker's rush
2. : a three-square file