morning: [13] The Old English word for ‘morning’ was morgen. It came from a prehistoric Germanic *murganaz (source also of German, Dutch, and Danish morgen ‘morning’), and links have been suggested with forms such as Old Church Slavonic mruknati ‘darken’ and Lithuanian mirgeti ‘twinkle’, which may point to an underlying etymological notion of the ‘glimmer of morning twilight’.
By the Middle English period the word morgen had evolved to what we now know as morn, and morning was derived from it on the analogy of evening. A parallel development of morgen was to Middle English morwe, from which we get modern English morrow (and hence tomorrow). => morn, tomorrow[morning etymology, morning origin, 英语词源]