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thereabouts (adv.)[thereabouts 词源字典]: early 15c., "in that area, around there; mid-15c., "near to that time, approximately thence," from Old English þær onbutan "about that place" + adverbial genitive -es; see there + about.[thereabouts etymology, thereabouts origin, 英语词源]
whereabouts (adv.): "in what place," early 15c., from whereabout + adverbial genitive -s. The noun, "place where someone or something is," is recorded from 1795. Whereabout in this sense is from c. 1600.