From Proto-Indo-European *mon- or *men-. Alternatively, Kroonen favors the word splitting off from Proto-Indo-European *dʰǵʰmō, *dʰǵʰmon- in the cases where the -m- wasn't syllabic (which otherwise gave *gum-, see *gumô), the initial cluster would have been unpronounceable in Germanic, giving a reduced *(-)man-.
This noun was inflected as a consonant stem, but the daughter languages disagree on the form of the nominative singular. The Gothic form points to a nominative *man(n)ô, as does the rare Old English nominative manna. The north and west Germanic forms, on the other hand, indicate *mannz. Judging from Gothic evidence, the original compounding form was *mana(n)- with only a single -n-, as in 𐌼𐌰𐌽𐌰𐍃𐌴𐌸𐍃 (manasēþs, “mankind”).
Several ideas have been proposed to explain the unusual morphology of this word, particularly the geminate -nn-. One proposal is that its stem was manwa- (wa-stem) or manu- (u-stem), where -nw- would have become -nn- through natural sound change in Germanic. This explains the relationship of the noun to cognates elsewhere in Indo-European, but crucially it does not explain the consonant stem inflection.
A more recent proposal is that the noun reflects a root man- to which n-stem endings have been added. These n-stem endings were not the usual type found in Germanic, but a rarer type that lacked a vowel between the root and the stem suffix in some of the forms. This is also seen in *uhsô (which has the stem *uhsn- in the plural), *arô (with *arn-), *berô (with *bern-) and Latin carō (with carn-). The stem without a vowel would have then been *man-n-, to which consonant stem endings would have been added, as n-stems were consonant stems in origin. If this is the case, it would explain the geminate -nn-, the consonant stem endings, and would also account for the n-stem nominative singular found in Gothic and Old English.
|consonant stemDeclension of *mann- (consonant stem)|
|nominative||*mann-, *manô, *mannô||*manniz|
- Old English: mann, ᛗ, man, monn, mon, manna
- Old Frisian: man, mon
- Old Saxon: man
- Old Dutch: man
- Old High German: man
- Middle High German: man
- Alemannic German: ma, mà, Maa, Mann, Mànn, mo, ma'
- Bavarian: mon, mònn, moon, ma'
- Central Franconian:
- Hunsrik: Mann
- East Central German:
- Silesian German: Moan
- German: Mann, man
- Luxembourgish: Mann
- Rhine Franconian:
- Pennsylvania German: Mann
- Yiddish: מאַן (man)
- Middle High German: man
- Old Norse: maðr
- Gothic: 𐌼𐌰𐌽𐌽𐌰 (manna)
- ^ Kroonen, Guus (2013) Etymological Dictionary of Proto-Germanic (Leiden Indo-European Etymological Dictionary Series; 11), Leiden, Boston: Brill