turn a hair, not

Not become afraid or upset, remain calm, as in She didn't turn a hair during the bank robbery. This term, also put as without turning a hair, comes from horse racing. After a race, a horse often has roughened, outward-turned hair. Its figurative use, nearly always in the negative, dates from the late 1800s.

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.