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This question on Latin.SE asks about the "elliptical dual", a construction where the dual number doesn't mean "two X" but instead "X and one other". For example, in the Iliad, Aíant-e Ajax-DUAL means not "the two Ajaxes" but "Ajax and Teucer".

Similarly (from the answers and comments on that question):

• Sanskrit ahanī day-DUAL "day and night"


• Latin Castor-ēs Castor-PLURAL "Castor and Pollux"


• Arabic al-qamarāni the-moon-DUAL "the sun and moon"

From my rudimentary knowledge, Japanese also seems to have a similar construction: Yuki-chan-tachi Yuki-DIM-PLURAL "Little Yuki and her friends".

I'm curious how widespread this phenomenon is. In English we don't seem to use the plural like this, but are we the outliers? Some of the examples here seem to come from Proto-Indo-European, but Arabic and Japanese certainly don't.

Since there are more languages with dedicated plural forms than there are with dedicated dual forms, this phenomenon is probably more common with plurals. I'm more familiar with constructions like Japanese "-tachi" being called "associative" plurals: there is a WALS chapter about this grammatical feature ("The Associative Plural", by Michael Daniel and Edith Moravcsik) which indicates that it is actually relatively widespread. Some languages have a distinct form used for associative plurals, but this appears to be less common.