/ ˌdɑːbi ən ˈdʒəʊn; NAmE ˌdɑːrbi ən ˈdʒoʊn/ noun
[ pl. ] ( BrE ) a way of referring to an old couple who are happily married
For more information see the Cultural Guide
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WORD ORIGIN
late 18th cent.: from a poem (1735) in the Gentleman's Magazine , which contained the lines “Old Darby, with Joan by his side ... They're never happy asunder.”