*ambô

Probably from Proto-Indo-European *h₃émbʰ-ō ~ *h₃m̥bʰ-nés, an n-stem formation belonging to root *h₃nebʰ-, with the *amb- traditionally explained as a Schwebeablaut/metathesized variant of *h₃nebʰ- (de Vaan 2008: 639; Kroonen 2013: 24; Wodtko et al. 2008: s.v. h₃nebʰ-). The closest cognate is Latin umbō, which continues the same n-stem; compare also Ancient Greek ὀμφαλός (omphalós), Sanskrit नाभि (nā́bhi), and Old Prussian nabis from the same root. The root also underlies *nabō ( < *h₃nobʰ-eh₂) and *nabalô, both from o-grade versions of the same PIE root (Lubotsky 2023: 257).

The PIE-level Schwebeablaut analysis is not certain: Ozoliņš (2015: 79–83) argues that the association of Old Saxon ambon with the *h₃nebʰ- family is itself not beyond doubt and that, if the etymology is accepted, the amb- shape could instead reflect Germanic analogical remodeling of an inherited ablauting n-stem. He nevertheless regards Latin umbō as the preferable direct comparison and notes that the semantic development ‘navel’ > ‘belly, abdomen’ is straightforward.