1. Pair, brace, couple, span, yoke are terms for groups of two. Pair is used of two things naturally or habitually associated in use, or necessary to each other to make a complete set: a pair of dice. It is used also of one thing composed of two similar and complementary parts: a pair of trousers. Brace is a hunter's term, used of a pair of dogs, ducks, etc., or a pair of pistols or slugs: a brace of partridges. In couple the idea of combination or interdependence has become greatly weakened; it may be used loosely for two of anything ( a couple of apples ), and even for more than two: I have to see a couple of people. Span is used of a matched pair of horses harnessed together side by side. Yoke applies to the two animals hitched together under a yoke for drawing and pulling: a yoke of oxen.

Did you mean unimpaired?