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    Old Irish (600-900)

The period of early Irish for which remains are available in the Roman alphabet begins after the Christianisation of Ireland in the 5th century. The first documents are glosses and marginalia from the mid-8th century contained in manuscripts found on the continent in the missionary sites of the Irish (Thurneysen 1946, Quin 1975). These were in Germany (Codex Paulinus in Würzburg), Switzerland (Codex Sangallensis in St. Gall with the glossed version of Priscian’s grammar) and northern Italy (Codex Ambrosianus in Milan). This period lasted until the end of the 9th century. The single external event which was most responsible for the demise of insular Old Irish was the coming of the Vikings in the late 8th century.

By considering Latin loan-words in Irish one can see that part of the phonological makeup of the language was the lenition which had begun during the Ogham period, e.g. lebor /ljevər/, later /ljaur/, from liber ‘book’, sacart /sagart/ from sacerdos ‘priest’.

The same applies to the Scandinavian loan-words towards the end of the first millennium margadh /margað/ later /margə/ from markaðr ‘market’. Phonological reduction can also be seen in cluster simplification as in fuinneog /fɪnjo:g/ from vindauga ‘window’. These developments continue well into the Middle Ages so that with Anglo-Norman loan-words from the 13th and 14th centuries one has similar lenition, e.g. the voicing evidenced by bagún from bacun ‘bacon’ or buidéal from botel ‘bottle’.

In Old Irish there is also a phenomenon called vowel affection, a change in vowel height as determined by the vowel in the following syllable, a type of Umlaut which remained a characteristic of the language for a considerable time, /o/ became /u/ before a following /i/ and /u/ became /o/ before a following /a/ or /o/. However, these vowel changes never attained grammatical status as Umlaut did in Germanic.

The main work on Old Irish is still the classic study by Rudolf Thurneysen (1857-1940). It first appeared as Handbuch des Altirischen in 1909 and was later translated into English, appearing in 1946 as A grammar of Old Irish.


The standard work on the vocabulary of Old (and Middle) Irish is the Dictionary of the Irish language based mainly on Old and Middle Irish materials. 1913–75; Compact edition, E. G. Quin (ed.), 1983 published by the Royal Irish Academy in Dublin.

There is a modern Irish index by Tomás de Bhaldraithe to the Dictionary of the Irish language which makes it easy to trace the etymology of a large amount of words in the present-day language.

As of Summer 2007 the Dictionary of the Irish language has been available online in a searchable form. To access this, use the following link.

eDIL website