One of the things which fascinate me about language is how one train of thought or trail of investigation can lead somewhere unexpected very quickly. Yesterday, while investigating ‘ploughman’s board’, I read the following sentence on Wikipedia: ‘Beer, bread, and cheese have been paired in the English diet since antiquity.’ I commented in a footnote that as far as I knew, a pair was always two and no more. The few dictionaries I’ve looked in support me in this, except perhaps for one which I’ll come back to in a moment.
Google Ngram Viewer gives ‘a pair of shoes, scissors, boots, gloves, compasses, horses, forceps, pistols’, which are all definitely two (or two halves) (as well as ‘a pair of small’ and ‘a pair of large’). ‘A pair of compasses’? Why would anyone need two compasses to find north? They don’t; the reference is to the circle-drawing implement used for maths instruction and navigation. The usage of the phrase has been declining since the 1890s. Even then, it was used far less than ‘a compass’, partly because ‘a compass’ encompasses both the direction-finding and the circle-drawing implements, whereas ‘a pair of compasses’ only refers to the latter. (Not surprisingly, ‘a pair of horses’ has also been declining in use.)
The only dictionary definition I could find which might possibly include more than two items is ‘20. to unite in close association with another, as in a business partnership, friendship, marriage, etc.’