Definition of: r, R

(är) noun plural r's, R's or rs, Rs, ars (ärz)
1. The 18th letter of the English alphabet: from Phoenician resh, Greek rho, Roman R.
2. The sound of the letter r. See ALPHABET.
—symbol
1. Chem. An organic radical.
2. Math. Ratio.
3. Electr. Resistance.
—the three R's Reading, writing, and arithmetic (regarded humorously as spelled reading, 'riting, and 'rithmetic); hence, the essential elements of a primary education.