While the connection between the words sweater and pullover and the clothes item they refer to is very clear, with the word jumper however, the relationship is rather vague: are people likely to jump when wearing jumpers?
marked as duplicate by coleopterist, Jasper Loy, tchrist, Andrew Leach, Matt Эллен Jan 2 '13 at 14:27
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The Oxford English Dictionary suggests that jumper is a form of the obsolete jump, which described various kinds of garment. It in turn may be a corruption of French juppe, which gave us English jup, also obsolete, and which was ‘assimilated by popular etymology to jump.’