mónaþ

Part of speech: noun
Gender: masculine
Stem: root stem
month (also mónað, mónoþ, mónoð, móneð, mónð)
Etymology
[Mod E MONTHProt-Germ *mēnōþ (← *mēn- “moon” + *-ōþ suff); Goth mēnōþs; O Fris mōnath; O Sax mānuth; Dt maand; OHG mānōd (Mod G Monat); O Icel mánaðr, mánuðr (Mod Icel mánuður)]
Paradigm

1.3. root-stem nouns

In Proto-Germanic (like in Gothic), this class of nouns was characterized by the addition of case endings immediately to the roots of the nouns in question. That is, nouns of this type did not have any stem-forming suffixes and had always had two-morpheme (root + case ending) structure.
The OE root-stem nouns are also characterized by vowel gradation. Consequently, the difference between their case-forms is grammatically marked both by means of case endings and the vocalization of their case and number forms.

root-stem nouns, masculine gender
mon
(man)
singular plural
nominative mon, monn men, menn
genitive monnes monna
dative (instrumental) men, menn mannum
accusative mon, monn men, menn

short-stemmed version: hnut-

root-stem nouns, feminine gender
hnutu
(nut)
singular plural
nominative hnutu hnyte
genitive hnute hnuta
dative (instrumental) hnyte hnutum
accusative hnutu hnyte

long-stemmed version: bóc-

root-stem nouns, feminine gender
bóc
(book)
singular plural
nominative bóc béc
genitive béc, bóce bóca
dative (instrumental) béc bócum
accusative bóc béc

Although the class of root-stem nouns in the OE incuded a very small number of nouns, this type of form building is the most well preserved in the Mod E: cf footfeet, goosegeese, louselice, manmen, mousemice, toothteeth.