D defs.my
Entry 1 sense Webster, 1913

Straightedge

/strāt'-ĕjˌ/ · Straight·edge · IPA /strˈeɪtˌɛdʒ/
01 n. A board, or piece of wood or metal, having one edge perfectly straight, -- used to ascertain whether a line is straight or a surface even, …
  1. 1.
    A board, or piece of wood or metal, having one edge perfectly straight, -- used to ascertain whether a line is straight or a surface even, and for drawing straight lines.