spiritus lenis

A diacritic mark that in Greek indicates smooth breathing. For example, when it is placed over an initial vowel it shows that it is not aspirated.

Etymology -
In Latin spiritus means "breath" and lenis "soft or mild"

Oxford English Dictionary -
Its first English citation is from 1867:
"Sanskrit v is generally represented in Greek by the Digamma, or the spiritus lenis."
(Max Müller Chips from German Workshop II. 87 )

Please comment