From Middle High German mōnōt, mānōt, from Old High German mānōd, from Proto-Germanic *mēnōþs, from a derivative of Proto-Indo-European *mḗh₁n̥s (“moon, month”). See also Mond. Compare Old Saxon mānoth, Dutch maand, English month, Danish måned.
Declension of Monat
- Monat in Duden online