Wiktionary
n. A handkerchief used as an accessory to a suit.
Usage examples of "pocket square".
He had on a well-cut but old-fashioned double-breasted blue serge suit, starched white shirt, linen pocket square, Windsor-knotted navy tie, and mirror-bright black bluchers with extra heel.
It hit the pocket square on and bounced back onto the felt, leaving the cue ball set up for a nice slightly off-straight shot at the one ball in the right side pocket.
From my window I could see him hurry down the street, a little black angry thing, very hot and troubled because he cannot measure the whole universe with his pocket square and compasses.
McDermott's got on this wool suit by Lubiam with a linen pocket square by Ashear Bros.
Spencer Wingate decked out in a blazer with an ascot and matching pocket square.
A pocket square that matched the shirt peeped from his breast pocket.
Asset in London, and a reasonably sober necktie and pocket square from the same people.
He was dressed in a navy suit, a white shirt, moire tie, a pocket square.