Instead of following astronomical seasons (beginning, in the Northern Hemisphere, on the equinoxes and solstices), or the meteorological seasons (beginning on March 1, June 1, September 1 and December 1), the irish calendar centres its seasons around the solstices and equinoxes. This means that, for instance, midsummer falls on the summer solstice. Seasons begin approximate halfway between solstice and equinox, following the seasons of the ancient Celts which are pre-Christian in origin.
This Celtic origin is particularly evident in the Irish naming of many of the months: some names were the names of pagan Celtic festivals, like May (Bealtaine), August (Lughnasadh/Lúnasa) and November (Samhain).
In addition, the names for September and October (Meán Fómhair and Deireadh Fómhair respectively) translate directly as "middle of autumn" and "end of autumn". Christianity has also left its mark on the Irish months: December is Nollaig, a word also meaning Christmastide.
- November, Samhain or Mí na Samhna
- December, Nollaig
- January, Eanáir
- February, Feabhra
- March, Márta
- April, Aibreán
- May, Bealtaine
- June, Meitheamh
- July, Iúil
- August, Lúnasa
- September, Meán Fómhair
- October, Deireadh Fómhair
Weekdays, Laethanta na Seachtaine
- Monday: An Luain or Dé Luain, Latin Lunae, "of the Moon"
- Tuesday: An Mháirt or Dé Máirt, Latin Martis, "of Mars"
- Wednesday: An Chéadaoin or Dé Céadaoin, Old Irish, "first fasting"
- Thursday: An Déardaoin or Déardaoin, Old Irish, "day between fastings"
- Friday: An Aoine or Dé hAoine, Old Irish, "fasting"
- Saturday: An Satharn or Dé Sathairn, Latin Saturni, "of Saturn"
- Sunday: An Domhnach or Dé Domhnaigh, Latin Dominica, "of the Lord"
Seasons of the year, Ráithí na Bliana/Na Séasúir
- Spring: An tEarrach, Spring/Vernal Equinox: Lá Leathach an Earraigh
- Summer: An Samhradh, Summer Solstice: Grianstad an tSamhraidh
- Autumn: An Fómhar, Autumnal Equinox: Lá Leathach an Fhómhair
- Winter: An Geimhreadh, Winter Solstice: Grianstad an Gheimhridh
Religious seasons, Séasúir Creidimh
- Lent: An Carghas, Latin Quadragesima, "fortieth"
- Easter: Cáisc, Latin Pascha (from Greek, from Aramaic, "passover")
- Advent: An Aidbhint, Latin Adventus, "coming"
- Christmastide: Nollaig, Latin Natalicia, "birthday celebration"
- Quarter Tense: Laethanta na gCeithre Thráth, "the days of four times"