Mainland

wiktionary

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From Middle English mayne londe; equivalent to main +‎ land. Compare Scots mayn-land, magan-land, madin-land(“mainland”), Faroese meginland(“mainland”), Icelandic meginland(“mainland”).

etymonline

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mainland (n.)

c. 1400, mainlond, "continent, principal land," from main (adj.) + land (n.). Usually referring to continuous bodies of land and not islands or peninsulas. Related: Mainlander. Mainland China, referring to the People's Republic (as opposed to Taiwan) is attested by 1955.