bump·kin1 (bmpkn, bm-) KEY
Perhaps from Flemish boomken, shrub, diminutive of boom, tree; see bheu- in Indo-European roots, or from Middle Dutch bommekijn, diminutive of bomme, barrel
The term bumpkin may at one time have been directed at an entire people rather than that segment of the population living in a rural area. The first recorded appearance of the word in 1570 is glossed by the Latin word Batavus, "Dutchman," making plausible the suggestion that bumpkin may come from either the Middle Dutch word bommekijn, "little barrel," or the Flemish word boomken, "shrub." The connection would be between a squat object and the short rotund figure of the Dutchman in the popular imagination. Any bumpkin would surely prefer this etymology to the suggestion that bumpkin is a derivative of bum, "the rear end."