From Longman Dictionary of Contemporary Englishsquare your shoulderssquare your shouldersDETERMINEDto stand straight and push your shoulders back, usually to show your determination → square
Examples from the Corpus
square your shoulders• Pulling himself upright, he squared his shoulders.• She got back on Midnight, in order to look down on Sebastian and Antony, and squared her shoulders.• Then she squared her shoulders and headed indoors.• She threw her head back, squared her shoulders and walked briskly toward the elevator.• She hesitated on the back steps a minute, then squared her shoulders and went inside.• I squared my shoulders, returned to the flat and cleaned the kitchen. 