íaru

Old Irish

Possibly from Proto-Celtic *wiweros.^[1] Alternatively, an "individualising" n-stem meaning "swift one", derived from Proto-Celtic *isaros (“swift”) (a word attested in the names of many rivers in Europe^[2]), from Proto-Indo-European *h₁ish₂ro-, for which compare Sanskrit इषिर (iṣirá-, “swift”) and Ancient Greek ἱερός (hierós, “supernatural”).^[3]

íaru f (genitive íarann, nominative plural íaranna)

Feminine n-stem
	Singular	Dual	Plural
Nominative	íaru	íarainn^L	íarainn, íaranna
Vocative	íaru	íarainn^L	íarna^H
Accusative	íarainn^N	íarainn^L	íarna^H
Genitive	íarann	íarann^L	íarann^N
Dative	íarainn^L, íaru^L	íarnaib	íarnaib
Initial mutations of a following adjective: ^H = triggers aspiration ^L = triggers lenition ^N = triggers nasalization

Old Irish mutation
Radical	Lenition	Nasalization
íaru	unchanged	unchanged
Note: Some of these forms may be hypothetical. Not every possible mutated form of every word actually occurs.

^ Matasović, Ranko (2011 December) “Addenda et corrigenda to Ranko Matasović’s Etymological Dictionary of Proto-Celtic (Brill, Leiden 2009)”, in Homepage of Ranko Matasović‎^[1], Zagreb, page 43
^ Delamarre, Xavier (2003) “isara”, in Dictionnaire de la langue gauloise: une approche linguistique du vieux-celtique continental (Collection des Hespérides; 9), 2nd edition, Éditions Errance, →ISBN, page 192
^ Sabine Ziegler (2002) “Altirisch íaru, das 'flinke' Eichhörnchen”, in Matthias Fritz, Susanne Zeilfelder, editors, Novalis Indogermanica: Festschrift für Günter Neumann zum 80. Geburtstag, Graz: Leykam, →ISBN, pages 537-39