Soho and Tribeca are both words invented by the real estate industry. "Soho" is from "South of Houston" and was intended to give the area south of what's now considered Greenwich Village some of the cachet of the Village. The fact that the name was identical with that of a fashionable area of London no doubt wasn't a coincidence. "Soho" succeeded so well in improving porverty values in its area that the real estate peddlers came up with "Tribeca" ("the Triangle below Canal") for another.
As for the L train, the letters designating the various subway lines don't signify anything. The "El" is another matter. During the first half of the 20th C., some of the subway lines in Manhattan were not in fact "subway", but ran on trestles above the street, for instance the Bowery. They were noisy and polluting and were replaced by trains running in tunnels. These lines were called the "El", as in "elevated". In the outer buroughs, stretches of some of the lines are still on elevated tracks.
George A. Thompson
Author of A Documentary History of "The African
Theatre", Northwestern Univ. Pr., 1998.