Caibidil a hAon: The Noun (an tAinmfhocal)

what belongs to it?

• almost only feminine nouns except 3 masculine (im, sliabh, teach)
• end in slender or broad consonants.

forming the genitive:

• with a slender final consonant + -e:
  e.g.: coill - coille, súil - súile
• with a broad final consonant , palatalisation (Caolú) + -e:
  e.g.: bróg - bróige, lámh - láimhe, sliabh - sléibhe
• often the second syllable is omitted (syncopation):
  e.g.: obair - oibre, seamair - seimre
• -(e)ach (feminine, polysyllabic, also: teach) to -(a)í*:
  e.g.: gealach - gealaí, báisteach - báistí, teach - tí
• but monosyllabic words ending in-och, -each, -uach to -oiche, -eiche (or -í), -uaiche

* -(a)í is only the orthographically new written form for -(a)ighe, and with this, also these words fit into the general rule of "palatalisation + -e"
e.g.: teach - tí (früher tighe), gealach - gealaí (früher gealaighe)

forming the dative

• those with a broad consonant form the dative through palatalisation.  This dative form appears in Connamara also as the nominative form,
  e.g. fuinneog - fuinneoig, clann - clainn
• this dative is only for the following 5 words also to be found in the standard:
  lámh - láimh, bos - bois, bróg - bróig, cluas -cluais, cos - cois
• the dative singular form is identical to a nominative dual form, which only comes after the number two (dhá):
  e.g.: dhá bhróig = two shoes

formation of the nominative plural:

• mostly weak plural: suffix -a or -e 
  e.g.: long - longa, póg - póga, cloch - clocha, gaoth - gaotha, críoch - críocha
• less common strong plural:  suffixes -anna, -acha, -ta, -tha etc.
  e.g.: áít - áiteanna, fuaim - fuaimeanna, craobh - craobhacha, tonn - tonnta, tír - tíortha
  polysyllabic nouns ending in a slender consonant form their plural regularly with -í,
  e.g.: aimsir - aimsirí, oifig - oifigí, abairt - abairtí

formation of the genitive plural:

• in the weak plural: = nominative singular,  but always depalatalisation (Leathnú), i.e. broad final consonant
  e.g.: glúin - glún, súil - súl, binn - beann, cill - ceall, deoir - deor
• in the strong plural = nominative plural

"regular" declination (weak plural)

typical suffixes of the 2nd declension

examples