sibh

Irish

sibh (emphatic form sibhse, conjunctive and disjunctive)

you (plural), ye/you
Bhí sibh ansin. ― You were there.

Cloisim sibh. ― I hear you.

Unlike many European languages, Modern Irish does not distinguish between "familiar" and "polite" second-person pronouns. Sibh is used to address two or more people, regardless of how well known those people are to the speaker. It is no longer used to address one single person.
The emphatic form sibhse is also used as the vocative: Haigh sibhse! — "Hey you (all)!"

From Old Irish sib. Cognates include Irish sibh and Manx shiu.

sibh (emphatic sibhse)

sibh is used to address more than one person, or to address one person formally or politely, particularly if they are significantly older or of higher social rank than the speaker.
Grandparents, teachers and clergymen are addressed as sibh, and parents often are also. Addressing them as thu would usually be considered rude.
People significantly younger than the speaker, for instance a child addressed by a young adult, are never addressed as sibh. Children do not use sibh amongst themselves. Some people may find it uncomfortable to be addressed as sibh if they do not consider themselves to be significantly older than the speaker.
The use of sibh varies by dialect, with some places being stricter about its usage than others.

Edward Dwelly (1911) “sibh”, in Faclair Gàidhlig gu Beurla le Dealbhan [The Illustrated Gaelic–English Dictionary]‎^[1], 10th edition, Edinburgh: Birlinn Limited, →ISBN
Gregory Toner, Sharon Arbuthnot, Máire Ní Mhaonaigh, Marie-Luise Theuerkauf, Dagmar Wodtko, editors (2019), “sib”, in eDIL: Electronic Dictionary of the Irish Language

Number	Person (and gender)	Conjunctive (emphatic)	Disjunctive (emphatic)	Possessive determiner
Singular	First	mé (mise)		mo ^L m' before vowel sounds
	Second	tú (tusa)¹	thú (thusa)	do ^L d' before vowel sounds
	Third masculine	sé (seisean)	é (eisean)	a ^L
	Third feminine	sí (sise)	í (ise)	a ^H
	Third neuter	—	ea	—
Plural	First	muid, sinn (muidne, muide), (sinne)		ár ^E
	Second	sibh (sibhse)¹		bhur ^E
	Third	siad (siadsan)	iad (iadsan)	a ^E

	simple		emphatic
	singular	plural	singular	plural
First person	mi	sinn	mise	sinne
Second person	thu, tu¹⁾	sibh	thusa, tusa¹⁾	sibhse
Third person m	e	iad	esan	iadsan
Third person f	i	iad	ise	iadsan
^) sibh* and sibhse also act as the polite singular pronouns. ^*) To mark a direct object of a verbal noun, the derivatives of gam* are used. ¹⁾ used when following a verb ending in -n, -s or -dh.