UK, 1989—the practice of sending food destined for the British market for irradiation in a country, typically the Netherlands, where this process is permitted, in order to mask any bacterial contamination before it is put on sale—from ‘Dutch’ and the suffix ‘-ing’, forming nouns denoting an action
USA, Boston Morning Post, 26 May 1834—‘Dutch uncle’: a person giving firm but benevolent advice—unknown origin—perhaps an allusion to Calvinistic sternness
UK, 1788—denotes an auction in which the price is lowered by stages until a buyer is found—said to have been invented by the Dutch specifically as the best solution to selling tulip bulbs
‘double Dutch’, 19th century—from ‘Dutch’ in the sense of a language that few people can speak, and ‘double’ as a mere intensifier—‘High Dutch’, 17th century—loan translation from French ‘haut allemand’ (= ‘High German’), used in the sense of gibberish
USA—‘to go Dutch’ (1907): to have every participant pay their own expenses, or share expenses equally—via ‘to go Dutch treat’ (1887), from ‘Dutch treat’ (1873): a meal, etc., at which each participant pays their share of the expenses—from a German practice
UK, 1797—strength or confidence gained from drinking alcohol—alludes to the drinking habits ascribed to the Dutch—one of the phrases in which ‘Dutch’ is used derogatorily, largely because of the enmity between the English and the Dutch in the 17th and 18th centuries
mid-19th cent.—perhaps from a specific application of the general term of abuse ‘Frog’, aided by the shared initial consonant cluster in ‘French’ and ‘frog’