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.
pitāhamasya jagato mātā dhātā pitāmahaḥ, — I the Father of this world, the Mother, the Ordainer, the first Creator, the object of Knowledge, the sacred syllable OM and also the Rik, Sama and… 9·17
माताmātānominative singular of the feminine noun mātṛ (the mother).