Midnight

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Old English midniht (see mid-, night).

wiktionary

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From Middle English midnight, midnyght, mydnyght, (also as middelniȝte), from Old English midniht, middeniht, middeneaht, (also as midderneaht and middelniht), from Proto-Germanic *midjanahts(“midnight”), equivalent to mid- +‎ night. Cognate with Saterland Frisian Midnoacht(“midnight”), Old High German mittinaht(“midnight”), Danish midnat(“midnight”), Swedish midnatt(“midnight”), Icelandic miðnætti(“midnight”). Compare also Saterland Frisian Middernoacht(“midnight”), Dutch middernacht(“midnight”), German Mitternacht(“midnight”).

etymonline

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midnight (n.)

"the middle of the night, 12 o'clock at night," Old English mid-niht, or middre niht (with dative of adjective). See mid (adj.) + night. Compare similar formation in Old High German mittinaht, German Mitternacht. Midnight oil symbolizing "late night work" is attested from 1630s.