The term 'soft low voice' can be summarized by the word 'CROON, ' which is a five-letter word. Crooning is a style of singing that is characterized by a gentle, low-pitched vocal delivery. It is often used in popular music, such as jazz and blues, as well as in folk music. The term is derived from the Old English word 'CRONE, ' which means to hum or murmur. Crooning has been around since the early 20th century and is still popular today.