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 शास्तृ
शास्तृśāstṛm.A teacher, an instructor.
[शास्-तृच् इडभावः]
A teacher, an instructor.
A ruler, king, sovereign.
A father.
A Buddha or Jina; or a deified teacher of the Bauddhas or Jainas.