In the antique trade, you often hear of "harlequin" pairs. But what exactly does that mean? No, it's not a sneaker, at least not to antiquarians:
I always thought a harlequin meant a clown and actually it does. Here's the harlequin clown as depicted by Picasso in 1918:
The term originally referenced the clown figure Arlecchino in the Italian traveling art troupe known as the Commedia dell' Arte (dating back to the 16th century). That figure is traditionally represented wearing diamond patterned multi-colored tights. Paul Cezannes' painting, Harlequin demonstrates this patterned motif and character:
But antiquarians use the term harlequin to mean a pair of items that are similar but not exactly matching. My guess is that this comes from the harlequin pattern where the diamonds match but the colors do not, hence they too are similar but not matching.
Here is a harlequin pair of 18th century Dutch brass candlesticks. Note how at first they appear identical but on closer inspection the triangular bases are of different sizes and the nozzle stems for the candles also differ in shape:
Another example would be this pair of late 18th century Louis XIV French Walnut Armchairs. Can you see how they differ?
The chair on the left has a shaped stretcher between the two front legs, unlike its harlequin twin on the right. And the shape of the arms differ in that the one on the left has more pronounced front portions curving down than does the one on the right.
Similar but not matching antiques like these are called "harlequin" pairs or sets.