An aspirated sound or letter; the diacritic (῾) used in polytonic Greek orthography to show that a letter (typically an initial vowel or rho) is aspirated; a rough breathing. Hence (occasionally): this symbol or another used similarly in writing another language.
spiritus asper/ˌspɪrɪtəs ˈaspə/ /ˌspɪrɪtʊs ˈaspɛː/
Mid 17th century. From post-classical Latin spiritus asper from classical Latin spīritus breath, aspiration, spirit + asper, after Hellenistic Greek πνεῦμα δασύ.