Las Vegas means "The Meadows." An easy way to remember it is, "The Veggies."
It was named in 1829 by one Rafael Rivera, a scout in the party of Antonio Armijo, a Mexican trader traveling on the Old Spanish Trail from Santa Fe to southern California (which had been blazed in 1776 by two Franciscan friars). Rivera discovered a shortcut along the route by way of Big Springs; he was the first non-Indian to set foot on the land that he called Las Vegas, for its life-saving water and soul-soothing greenery.