Month
Old English mōnath, of Germanic origin; related to Dutch maand and German Monat, also to moon.
wiktionary
From Middle English month, moneth, from Old English mōnaþ(“month”), from Proto-Germanic *mēnōþs(“month”), from Proto-Indo-European *mḗh₁n̥s(“moon, month”), probably from Proto-Indo-European *meh₁-(“to measure”), referring to the moon's phases as the measure of time, equivalent to moon + -th. Cognate with Scots moneth(“month”); North Frisian muunt(“month”); Saterland Frisian Mound(“month”), Dutch maand(“month”); German Low German Maand, Monat(“month”); German Monat(“month”); Danish and Norwegian Bokmål måned(“month”); Norwegian Nynorsk and Swedish månad(“month”); Icelandic mánuði(“month”); Latin mēnsis(“month”); Ancient Greek μήν(mḗn); Armenian ամիս(amis); Old Irish mí; Old Church Slavonic мѣсѧць(měsęcĭ). See also moon.
etymonline
month (n.)
"one-twelfth part of a year; one of the twelve parts into which the calendar year is arbitrarily divided," Old English monað, from Proto-Germanic *menoth- (source also of Old Saxon manoth, Old Frisian monath, Middle Dutch manet, Dutch maand, Old High German manod, German Monat, Old Norse manaðr, Gothic menoþs "month"), which is related to *menon- "moon" (see moon (n.)). Originally the month was the interval between one new moon and the next (a sense attested from late Old English).
Its cognates mean only "month" in the Romance languages, but in Germanic they generally continue to do double duty. The development of the calendrical meaning for words from this root in Greek (mēn) and Latin (mensis) was accompanied by the creation of new words for "moon" (selēnē, luna). The phrase a month of Sundays "a very long time" is from 1832 (roughly 7 and a half months but never used literally).
