V. S. Apte, The Practical Sanskrit–English Dictionary. Look up any word of the Gita in Devanagari, IAST or Harvard-Kyoto, or browse the headwords letter by letter.
Entry अतस
अतसatasaWind, air.
[अतति गच्छति इत्यतसः अत्-असच् Uṇ.3.117]
Wind, air.
The soul.
A garment made of the fibre of flax (denotes that the rest of the word under consideration is to be suppliedसं generally).