Definition of "RI"

Initialism of Rhode Island, a state of the United States of America.  examples

Abbreviation of Riau, a province of Indonesia.  examples

Initialism of radioisotope.  examples

Initialism of radio interference.  examples

(monarchy) rex imperator (“king-emperor”) or regina imperatrix (“queen-empress”); the initials by which a British monarch signed documents after his or her name from 1877 until 1947.  examples