STRAIGHTEDGE
straightedge
(noun) hand tool consisting of a flat rigid rectangular bar (metal or wood) that can be used to draw straight lines (or test their straightness)
Source: WordNet® 3.1
Adjective
straightedge (comparative more straightedge, superlative most straightedge)
Living one's life opposing or eschewing the use of drugs such as alcohol and tobacco.
Noun
straightedge (plural straightedges)
A flat, rectangular tool used to draw, cut or check the straightness of straight lines.
Source: Wiktionary
Straight"edge`, n.
Definition: 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.
Source: Webster’s Unabridged Dictionary 1913 Edition