Definition of Darby and Joan in English:

Late 18th century: 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.’.

• An anonymous poem of 1735 in The Gentleman's Magazine contained the lines: ‘Old Darby, with Joan by his side, / You've often regarded with wonder: / He's dropsical, she is sore-eyed, / Yet they're never happy asunder.’ People quickly began to use the names, whose exact origin is unknown, for any devoted old married couple.