fifty的序数词是fiftieth。fiftieth的意思是第五十。fiftieth的例句That\'s the fiftieth Christmas card I\'ve written（这是我写的第五十张圣诞卡）。
fiftieth的例句He was stricken by a heart attack on his fiftieth birthday（他在五十岁生日那天心脏病发作）；He retired in 1970, on his fiftieth birthday（他在1970年自己50岁生日时退了休）。
