A dozen or so river names across Europe may descend from something like *navis.
While discussing Φλαουιοναουια, Garcia Alonso (2001:218) wrote:
“Navia is frequent as a river name, and as a place name, with examples in the Iberian Peninsula, France, Britain, Germany and Lithuania ... and fits well in the Alt-europäisch hydronymy ... It could be the same root we see in Sanskrit navya , ‘navigable’, Old Persian naviya ‘fleet’, Greek νηιος ‘concerning a ship’, all from Indo-European *naus-‘ship’ ... It is possible to relate this to nava ‘valley’, widely used throughout the Iberian Peninsula ... and in other areas of Western Europe (the Dolomitic Alps, Corsica). The metaphoric use of a word meaning ‘ship’ to designate a valley has parallel examples: Barco in the toponymy of Castille ..... Navia is almost unanimously considered pre-Celtic Indo-European Alt-europäisch in fact.”
English and French combe ‘valley’, related to Latin cumba ‘boat’ and to words in Greek, Sanskrit, etc meaning ‘bowl, bottom of ship’, is another example of that metaphor. It is unlikely that Welsh cwm existed early enough to be the source of English combe.
While discussing Navio, R&S cited PIE *sna- ‘to flow’, hence Welsh nawf, nofio , ‘to swim’ and Latin no, nare. So they proposed a British river-name *Nav- ‘fast-flowing water’, related also to the German river Nahe (from Nava) near Bingen.
For Ptolemy's Ναβαρου, the modern Naver in northern Scotland, Watson (1927: 47) proposed an origin in PIE *nebh- ‘cloud’, hence νεφος, or Sanskrit nabhas, or nebula or nimbus.
Early names in Britain that may include *navis include Anava (river Annan), Brinavis (Brentford), Naurum (Barnstaple Bay), Navione (Brough-on-Noe), Purocoronavis (?Bude), Κορναουιοι (tribe with towns at Chester and Wroxeter), Κορναουιοι (tribe in north-east Scotland), and Manavi (near Clackmannan etc).
With a change of vowel from A to O there are Durocornovium, the Νοουανται tribe in Galloway, the Τρινοαντες tribe in East Anglia, Durnonovaria (Dorchester), Novitia (river Esk), and Novia (Chichester Harbour).
Less likely cases include Anderelionuba (Pevensey), Navimago Regentium (Chichester), Noviomagnus (?Old Sarum), Noviomagus (West Wickham), Panovius (unlocated), and Vinovium (Binchester).
Overseas examples include Αναβον/Αναυον (Komarno, Danube/Vah confluence, Slovakia), Ναυαλια (Essen, on the Ruhr), Νουαισιον/Ναυαισιον (Melsungen, on the Fulda), Ναβιου (river Eo, Spain), Νηβιος (river Cavado, Spain).
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