Noun
spiritus asper (plural spiritus aspers)
(orthography) A diacritic mark ( ʻ ) in Ancient Greek used to indicate aspiration of an initial vowel or rho; also used for a similar sound in the Wade–Giles system of romanization for Mandarin Chinese.
The spiritus asper mark looks like an opening single quote, as in the word εὑρίσκω (heurískõ), the word εὕρηκα (heúrēka), or the word ἕξις (héxis, "habit").