The spiritus asper ("rough breathing") or dasy pneuma (Greek: dasu, δασύ) is a diacritical mark used in Greek. It indicates an initial aspiration: in other words that the word began with an [h] sound in in Ancient Greek. It is written as on top of or to the left of an initial vowel (the second vowel of a pair comprising a diphthong), and also on an initial rho or the second of a pair of rhos. It takes the form of an opening half moon or an opening single quotation mark:

• ἁ- ἑ- ἡ- ἱ- ὁ- ὑ- ὡ- ῥ-;

• Ἁ- Ἑ- Ἡ- Ἱ- Ὁ- Ὑ- Ὡ- Ῥ-.

The only situations when it can be written inside a word are :

• on a double rho in certain editions;
• when it represents a coronis resulting from a crasis implying a vowel bearing a spiritus asper.

The spiritus asper merely notes the presence of an initial consonant [h], which cannot be written otherwise when it is not initial: thus ὕμνος stands for humnos, "hymn", and ῥήτωρ for hrêtôr (or rhêtôr), "orator".

When a word begins by an initial grapheme which is a vowel not preceded by an [h], the spiritus lenis ("soft breathing") is employed.

It is part of the traditional polytonic orthography for Greek, but has been dropped in the modern monotonic orthography as the [h] sound has disappeared from Modern Greek. The origin of the sign is thought to be the left-hand half ( ├ ) of the letter H, which was used in some Greek dialects as an [h] while in others it was used for the vowel eta.

Dasia pneumata were also used in the early Cyrillic alphabet when writing the Old Church Slavonic language. In this context it is encoded as Unicode U+04805 or HTML entity ҅ ( ◌҅ ).

See also

• Spiritus lenis
• Polytonic Greek orthography