English▸ noun (chiefly in military contexts) a turn made so as to face the opposite direction:
he did an about-face and marched out of the tent.
▪ a complete change of opinion or policy:
he threatened to stop helping us, but did a complete about-face.
▸ verb [no object] turn so as to face the opposite direction:
protestors retreated, about-faced, and resumed chanting.
▸ (about face!) exclamation (in military contexts) a command to turn so as to face the opposite direction.
– ORIGIN early 19th century (originally as a military command): earlier in right about face.