inked marking string; standard
Refers to a carpenter's inked string used for marking straight lines, and by extension a standard or rule. The 'standard' sense is a figurative extension of the tool.
The carpenter used an inked marking string to draw a straight line on the lumber.
His behavior deviates from the standards of society.
Compound of 縄 (rope, cord) and 墨 (ink). Originally referred to the inked string used by carpenters to mark straight lines, later extended metaphorically to mean a standard or rule.