Longman Dictionary of Contemporary English - fifty number

1 50 2 the fifties a) the years between 1950 and 1959  (Standards of living rose in the fifties.) b) the numbers between 50 and 59  (especially when used to measure temperature)  (sunny, with temperatures in the mid fifties) 3 be in your fifties to be aged between 50 and 59  (early/mid/late fifties)  (He must be in his early fifties by now.) 4 a piece of paper money equal to fifty dollars or fifty pounds