idir

• eadair, eadar (Ulster)
• eidir (Connacht)

From Old Irish eter,[1] from Proto-Indo-European *h₁enter (“between”). Cognate with Latin inter (“between”) and Sanskrit अन्तर् (antár, “between, within, into”). Compare Scottish Gaelic eadar.

• (Munster) IPA^(key): /ˈɪdʲəɾʲ/[2]
• (Galway) IPA^(key): /ˈɛdʲəɾʲ/[3] (corresponding to the form eidir)
• (Ulster) IPA^(key): /ˈɛd̪ˠəɾʲ/[4] (corresponding to the form eadair)

idir (plus nominative in singular, dative in plural, triggers lenition except in certain constructions with distance, time, difference, or opposition)

1. between

   idir fhir agus mhná ― between men and women

   • 2014, Bruno Coulais (lyrics and music), “Amhrán Na Farraige [Song of the Sea]”:

     Idir ann is idir as. Idir thuaidh is idir theas.

     Between in and between out. Between north and between south.

2. both (paired with agus (“and”))

   idir chait agus mhadraí ― both cats and dogs

3. partly...partly..., half...half... (paired with agus (“and”))

   idir bheith ag caint agus chanadh ― half talking, half singing

• In modern usage, has inflected forms only in the plural. Is used with nouns and singular pronouns in combination with another noun or pronoun:

idir é agus mé ― between him and me

• In the sense of strictly "between", does not trigger lenition when a definite path can be traced between the things being described; often occurs with distance, time, and difference and almost always occurs with opposition:

idir Maigh Eo agus Gaillimh ― between Mayo and Galway

idir fómhar agus geimhreadh ― between autumn and winter

an difríocht idir maith agus olc ― the difference between good and evil

cogadh idir tíortha ― war between countries

cluiche idir Baile Átha Cliath agus Corcaigh ― a game between Dublin and Cork

But:

idir thithe ― between houses (indistinct, cannot be represented by a definite path)

idir shaoirí ― between holidays

cur idir dhaoine ― to interfere between people

• When mutation does occur, the s in agus blocks mutation of d, s, and t in the following word even though it is not the trigger:

idir Phádraig agus Tadhg ― between Patrick and Tadhg

idir rith agus siúl ― half running, half walking

idir shonas agus deora ― between happiness and tears

From Old Irish etir (“at all”),[1] originally 3rd person sg. neut. form of Old Irish eter (“between”).

• IPA^(key): /ˈitʲɪɾʲ/

idir

1. at all

   Chan eil idir. ― Not at all.

   Chan e idir. ― That is not it at all.

   Cha tig e idir. ― He will not come at all.

   No idir air a bhruicheadh. ― Nor even boiled.

   Chan eil e gu math idir. ― He is not at all well.

   Cha deanainn idir e. ― I would not do it on any account.

   Cha toil leam purpaidh idir. ― I don't like purple at all.

2. yet

• Edward Dwelly (1911) “idir”, in Faclair Gàidhlig gu Beurla le Dealbhan [The Illustrated Gaelic–English Dictionary]‎, 10th edition, Edinburgh: Birlinn Limited, →ISBN
• MacLennan, Malcolm (1925) A Pronouncing and Etymological Dictionary of the Gaelic Language, Edinburgh: J. Grant, →OCLC