Fifth Declension

The 5th declension is a group of mostly feminine nouns in Irish. It is considered an “irregular” declension because its nouns follow several different patterns, often involving a change from a slender to a broad consonant in the genitive case. This group includes common words like kinship terms and place names.

Nouns in this declension typically have one of the following characteristics:

• They are mostly feminine. Masculine nouns in this group often have a -d in the genitive singular.
• They end in a slender consonant, such as -il, -in, or -ir.
• They end in a vowel or in -inn or -in.
• They are terms of kinship ending in -ir, like athair (father), máthair (mother), and bráthair (brother, friar).

Genitive Singular

The genitive singular of 5th declension nouns always ends in a broad consonant. There are several ways this is formed, based on the noun’s historical stem.

Depalatalisation

The most straightforward pattern is the depalatalisation of the final consonant, where a slender consonant becomes broad.

• athair -> athar (father -> of a father)
• Albain -> Alban (Scotland -> of Scotland)
• abhainn -> abhann (river -> of a river)
• Nollaig -> Nollag (Christmas -> of Christmas)

Adding -ach or -each

Many nouns ending in -il, -in, or -ir form the genitive by depalatalising the final consonant and adding the ending -ach.

• beoir -> beorach (beer -> of beer)
• cathair -> cathrach (city -> of a city)

Polysyllabic nouns with a slender consonant in the second syllable often add -each instead, sometimes without depalatalisation. This frequently causes syncope (the loss of a vowel in the middle of the word).

• litir -> litreach (letter -> of a letter)
• uimhir -> uimhreach (number -> of a number)

Adding -n, -nn, or -d

Nouns that end in a vowel typically add -n, -nn, or -d in the genitive.

• cara -> carad (friend -> of a friend)
• pearsa -> pearsan (person -> of a person)
• Éire -> Éireann (Ireland -> of Ireland)
• caoga -> caogad (fifty -> of fifty)

Dative Singular

Historically, all dative forms in this declension ended in a slender consonant. In modern Irish, the dative singular is often replaced by the nominative singular form, but some dative forms remain in common use, especially after prepositions.

Historical Dative Forms

Some common 5th declension nouns are actually historical dative forms that have replaced the original nominative. For these words, the nominative and dative are identical.

• Éirinn (from Éire) is common in Connacht and Ulster.
• Albain (from Alba, which is still used in Scottish Gaelic).
• abhainn (from abha).

Palatalising the Genitive

Nouns with a genitive in -n, -nn, or -d form the dative by palatalising this ending (making it slender).

• Genitive fichead (of twenty) -> Dative fichid
• Genitive carad (of a friend) -> Dative caraid
• Genitive Éireann (of Ireland) -> Dative Éirinn

The dative form Éirinn is required after prepositions.

• in Éirinn - in Ireland (Correct)
• in Éire - in Ireland (Incorrect)

Palatalising -(e)ach

Nouns with a genitive in -(e)ach historically formed the dative by changing the ending to -(a)igh. This form is less common today and is often replaced by the nominative.

• Genitive caorach (of a sheep) -> Dative caoirigh
• Genitive beorach (of beer) -> Dative beoraigh

Nominative Plural

Genitive Form + -a

A common way to form the nominative plural is to take the genitive singular form and add -a. The plural endings -(e)acha and -(e)anna, now common in other declensions, originate from this pattern.

• cathair (city) -> cathrach (gen. sg.) -> cathracha (nom. pl.)
• comharsan (neighbour) -> comharsana (nom. pl.)

Exceptions

Some nouns have irregular plural forms.

• athair (father) -> aithreacha
• abhainn (river) -> aibhneacha

Genitive Plural

The genitive plural can be formed in two main ways:

• It is most often identical to the nominative plural.
• For some nouns, especially those with a genitive singular in -n or -d, it is identical to the genitive singular.

Declension Patterns

This table summarises the main patterns. The dative is omitted as it is mostly replaced by the nominative in modern usage.

Examples