From Proto-Turkic *yulduŕ (“star”). 'ҫтӑр' is the conglomerated form of 'ҫӑл' + 'тӑр'. See cognates at the Proto Turkic entry, compare also Turkish yıldırım.
ҫӑлтӑр • (śălt̬ăr) (plural ҫӑлтӑрсем)