Psilosis is the sound change

Sound change

Sound change includes any processes of language change that affect pronunciation or sound system structures...

 in which Greek

Greek language

Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 lost the consonant sound /h/ during antiquity. The term comes from the Greek psílōsis ("smoothing, thinning out") and is related to the name of the smooth breathing (ψιλή ), the sign for the absence of initial /h/ in a word. Dialects that have lost /h/ are called psilotic.

The linguistic phenomenon is comparable to that of h-dropping in dialects of Modern English, and to the development by which /h/ was lost in late Latin

Late Latin

Late Latin is the scholarly name for the written Latin of Late Antiquity. The English dictionary definition of Late Latin dates this period from the 3rd to the 6th centuries AD extending in Spain to the 7th. This somewhat ambiguously defined period fits between Classical Latin and Medieval Latin...

.

History

The loss of /h/ happened at different times in different dialects of Greek. The eastern Ionic

Ionic Greek

Ionic Greek was a subdialect of the Attic–Ionic dialect group of Ancient Greek .-History:Ionic dialect appears to have spread originally from the Greek mainland across the Aegean at the time of the Dorian invasions, around the 11th Century B.C.By the end of the Greek Dark Ages in the 5th Century...

 dialects, the Aeolic

Aeolic Greek

Aeolic Greek is a linguistic term used to describe a set of dialects of Ancient Greek spoken mainly in Boeotia , Thessaly, and in the Aegean island of Lesbos and the Greek colonies of Asia Minor ....

 dialect of Lesbos, as well as the Doric

Doric Greek

Doric or Dorian was a dialect of ancient Greek. Its variants were spoken in the southern and eastern Peloponnese, Crete, Rhodes, some islands in the southern Aegean Sea, some cities on the coasts of Asia Minor, Southern Italy, Sicily, Epirus and Macedon. Together with Northwest Greek, it forms the...

 dialects of Crete

Crete

Crete is the largest and most populous of the Greek islands, the fifth largest island in the Mediterranean Sea, and one of the thirteen administrative regions of Greece. It forms a significant part of the economy and cultural heritage of Greece while retaining its own local cultural traits...

 and Elis

Elis

Elis, or Eleia is an ancient district that corresponds with the modern Elis peripheral unit...

, were already psilotic at the beginning of their written record. In Attic

Attic Greek

Attic Greek is the prestige dialect of Ancient Greek that was spoken in Attica, which includes Athens. Of the ancient dialects, it is the most similar to later Greek, and is the standard form of the language studied in courses of "Ancient Greek". It is sometimes included in Ionic.- Origin and range...

, there was wide-spread variation in popular speech during the classical period, but the formal standard language retained /h/. This variation continued into the Hellenistic Koine

Koine Greek

Koine Greek is the universal dialect of the Greek language spoken throughout post-Classical antiquity , developing from the Attic dialect, with admixture of elements especially from Ionic....

. Alexandrine grammarians who codified Greek orthography during the second and first centuries BC, and who, among other things, introduced the signs for the rough and smooth breathings, were still using the distinction between words with and without initial /h/, but were evidently writing at a time when this distinction was no longer natively mastered by many speakers. By the late Roman and early Byzantine period, /h/ had been lost in all forms of the language.

Eta and heta

The loss of the /h/ is reflected in the development of the Greek alphabet

Greek alphabet

The Greek alphabet is the script that has been used to write the Greek language since at least 730 BC . The alphabet in its classical and modern form consists of 24 letters ordered in sequence from alpha to omega...

 by the change in the function of the letter Eta

ETA

ETA , an acronym for Euskadi Ta Askatasuna is an armed Basque nationalist and separatist organization. The group was founded in 1959 and has since evolved from a group promoting traditional Basque culture to a paramilitary group with the goal of gaining independence for the Greater Basque Country...

 (Η), which first served as the sign of /h/ ("Heta

Heta (letter)

Heta is a conventional name for the historical Greek alphabet letter Eta and several of its variants when used in their original function of denoting the consonant /h/. The letter Η had been adopted by Greek from the Phoenician letter Heth originally with this consonantal sound value, and Hēta...

") but then, in the psilotic dialects, was re-used as the sign of the long vowel /ɛː/.

Rough and smooth breathing

In the traditional polytonic orthography

Greek diacritics

Greek orthography has used a variety of diacritics starting in the Hellenistic period. The complex polytonic orthography notates Ancient Greek phonology...

 of Ancient Greek

Ancient Greek

Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...

, the original /h/ sound, where it used to occur, is represented by a diacritic

Diacritic

A diacritic is a glyph added to a letter, or basic glyph. The term derives from the Greek διακριτικός . Diacritic is both an adjective and a noun, whereas diacritical is only an adjective. Some diacritical marks, such as the acute and grave are often called accents...

, the rough breathing or spiritus asper. This sign is also conventionally used in analogy to the Attic usage when rendering texts from the Ionic dialect, which was already psilotic by the time the texts were written. For Aeolic texts, however, the convention is to mark all words as non-aspirated.