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small cucumber used for pickling, 1660s, from early modern Dutch gurken, augurken (late 16c.) "small pickled cucumber," from East Frisian augurk "cucumber," probably from a Balto-Slavic source (cf. Polish ogórek "cucumber"), possibly ultimately from Medieval Greek angourion "a kind of cucumber," said to be from Persian angarah [Klein, etc.], but OED seems to regard this as unlikely. A Dutch source says the Greek is from a word for "immature" and that the vegetable originated in northern India and came to Eastern Europe via the Byzantine Empire.
The Dutch suffix is perhaps the diminutive -kin, though some regard it as a plural affix, with the Dutch word mistaken for a singular in English. The -h- was added 1800s to preserve the hard "g" pronunciation.
(Cucumis anguria), trailing vine, of the gourd family (Cucurbitaceae), grown for its edible fruit. The gherkins sold in pickle mixtures are not C. anguria but rather are small pickled immature fruits of cultivars of the cucumber (C. sativus). A true gherkin has palmately lobed leaves with toothed edges, small flowers, and furrowed, prickly fruits about five centimetres (two inches) long that are borne on crooked stalks. Although its fruit is also pickled, the plant is frequently grown only as a curiosity.