PIE word
*swé
* Often derived from earlier *swolos, from Proto-Italic *swelos, from Proto-Indo-European *swé (reflexive pronoun) (whence se (“oneself”)) + *-los, hence meaning "by oneself";
* De Vaan refers it to *solh₂- (“whole, healthy”), which would make it akin to sollus and salvus.
* Others connect it with Proto-Germanic *sēliz (Gothic 𐍃𐌴𐌻𐍃 (sēls, “happy, good”), Old English sēlra (“better”)), from Proto-Indo-European *selh₂- (whence sōlor (“to console”)).