A special feature in the history of the hydronym Saar is that in the first centuries of its attestation up to the high Middle Ages it shows two parallel, morphologically different forms, Sar- vs. Sar-Vv-, the longer form being attested earlier. For the shorter form Sar- an Old European formation *Sorā- from a root PIE *ser- ‘(to be) liquid’ seems most probable. For the longer form actually three possibilities exist: either (a new proposal) it is a secondary u̯o-derivative of the aforementioned *Sorā-; or one of two different Celtic etymologies hitherto proposed applies: both claiming u̯o-derivatives, either (less probably) from the root PIE *serh- ‘to approach (with unfriendly intentions)’ or (more probably) from the root PIE *sterh3- ‘to stretch, spread, broaden’, both in the end resulting in Late Proto-Celtic *sarau̯o-. As the two attestations in a metrical text reflect Latin Sarāv-, at some point in the history of the name there seems to have been some (analogical) restructuring of the suffix vowel.