Abroad

google

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Middle English: from a-2 ‘on’ + broad.

wiktionary

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First attested in mid 13th century. From Middle English abrood(“broadly widely scattered”), from a-(“on, in”) + brood(“broad”). Equivalent to a- +‎ broad.

etymonline

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abroad (adv.)

mid-13c., "widely apart," a contraction of on brode, from Old English on brede, "in width," literally "at wide" (see a- (1) + broad (adj.)). From c. 1300 as "at a distance from each other," hence "out of doors, away from home" (late 14c.) also "at a distance generally" (early 15c.), and the main modern sense, "out of one's country, overseas" (mid-15c.).