<p><strong>Noun</strong></p><ul><li>A cardinal number, next after the third; being the ordinal number for four.</li><li>A fourth part, especially of one (¼).</li><li>The fourth member of a series.</li><li>Music: A tone on the fourth degree from a given tone (counted as the first).</li><li>The interval between such tones.</li><li>The harmonic combination of such tones.</li><li>Automotive: Fourth gear.</li><li>The Fourth: Independence Day; the Fourth of July.</li></ul><p><strong>Adjective</strong></p><ul><li>Being one of four equal parts.</li><li>Automotive: Of, relating to, or operating at the gear transmission ratio at which the drive shaft speed is greater than that of third gear for a given engine crankshaft speed, but not so great as that of fifth gear, if such exists: fourth gear.</li></ul><p><strong>Adverb</strong></p><ul><li>In the fourth place; fourthly.</li></ul>