tail off
phrasal verb with tail verb [ T ] uk/teɪl/ us/teɪl/
逐渐变小，逐渐减弱
to reduce in amount or become lower in level
His voice tailed off as he drifted into sleep. 他迷迷糊糊地快睡着了，说话声越来越小。
The profits tailed off after a few years. 几年后，利润越来越少。