Belong

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Old English belangian, of Germanic origin.

wiktionary

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From Middle English belongen, bilongen, from Middle English be- + longen(“to be fitting, be suitable”), from Old English langian(“to pertain to, suit”), equivalent to be- +‎ long(“to belong”). Compare Saterland Frisian beloangje(“to attain, reach, meet”), Dutch belangen(“to concern”), German belangen(“to attain, concern”).

Compare Kriol blanga, Bislama blong, Tok Pisin bilong, and Torres Strait Creole blong.

etymonline

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belong (v.)

mid-14c., "to go along with, properly relate to," from be- intensive prefix, + longen "to go," from Old English langian "pertain to, to go along with," which is of uncertain origin but perhaps related to the root of long (adj.). Senses of "be the property of" and "be a member of" first recorded late 14c. Cognate with Middle Dutch belanghen, Dutch belangen, German belangen. Replaced earlier Old English gelang, with completive prefix ge-.