The term "ohm" is named after the German physicist Georg Simon Ohm, who is best known for Ohm's Law, which relates voltage, current, and resistance in an electrical circuit. There isn't a "full word" for "ohm" per se—it's a unit of electrical resistance. The ohm is symbolized by the Greek letter omega (Ω).
In essence, "ohm" itself is not an abbreviation or shorthand for something else; it's a unit of measurement named in honor of Ohm's contributions to electrical theory.