From Old Irish fein, from Proto-Indo-European *swey-no-, suffixed form of root *swé, pronoun of the third person and reflexive (referring back to the subject of a sentence), also used in forms denoting the speaker’s social group, “(we our-)selves”.
mé féin ― myself(both emphatic and reflexive)
sinn féin ― ourselves; we ourselves
mo theach féin ― my own house
|Note: Some of these forms may be hypothetical. Not every
possible mutated form of every word actually occurs.