Couper les cheveux en quatre

Literally: To cut hair in four

Example: “On ne va pas couper les cheveux en quatre pour deux euros de différence.” — We're not going to split hairs over a two-euro difference.

English equivalent: To split hairs

Origin: The 17th century said fendre un cheveu en quatre — to split a hair in four — and an even older form only bothered to split it in two; Furetière's 1690 dictionary has that simpler version. By the end of the 18th century the ambition had grown to four, and the Académie française's 1798 dictionary already lists fendre un cheveu en quatre. Couper replaces fendre from the middle of the 19th century onward. The image needs no gloss: cutting a single hair along its width into four requires a precision no reasonable task calls for, which is exactly the accusation leveled at anyone who insists on it.