<p><strong>noun</strong></p><ul><li>plural: fifties.</li><li>a cardinal number, ten times five.</li><li>a symbol for this number, as 50 or L.</li><li>a set of this many persons or things.</li><li>fifties: the numbers, years, degrees, or the like, from 50 through 59, as in referring to numbered streets, indicating the years of a lifetime or of a century, or degrees of temperature:<ul><li>She lives in the East Fifties.</li><li>He's in his late fifties.</li><li>It's going to be in the fifties again today.</li></ul></li><li>Informal: a fifty-dollar bill: He had a fifty and two tens in his wallet.</li></ul><p><strong>adjective</strong></p><ul><li>amounting to 50 in number.</li></ul>