From Proto-Italic *galsos, enlargement of *gl̥s-o-, zero-grade of Proto-Indo-European *gols-o-, from *gelH- (“to call”); compare Proto-Balto-Slavic *galsas (“voice”), Proto-Germanic *kalzōną (“to call”), Albanian gjuhë (“tongue; language”), and perhaps Welsh galw (“call”).
Practice speaking and memorizing "gallus" and many other words and sentences in Latin.