tobann

Irish

Alteration of earlier obann, from Middle Irish opund (“quick, sudden”), ^[2] from Proto-Celtic *od-bond, of uncertain origin:

Possibly from the root of bonn (“foundation”).
According to Stokes, cognate with Old Church Slavonic абиѥ (abije, “immediately, at once”), Ancient Greek ἄφαρ (áphar, “at once”), ἄφνω (áphnō, “suddenly”).^[3]
Possibly instead related to Welsh buan (“swift, rapid”), from Proto-Indo-European *gʷeyh₃- (“to live”).

tobann (genitive singular masculine tobainn, genitive singular feminine tobainne, plural tobanna, comparative tobainne)

sudden, unexpected
hasty, quick
precipitate (with a hasty impulse), rash, snap (done quickly and unexpectedly), abrupt (without notice)
impetuous (making arbitrary decisions), impulsive (actuated by impulse or transient feelings)
irascible, quick-tempered, short-tempered

¹ When the preceding noun is lenited and governed by the definite article.
² When the preceding noun ends in a slender consonant.

Mutated forms of *tobann*
radical	lenition	eclipsis
tobann	thobann	dtobann

Note: Certain mutated forms of some words can never occur in standard Modern Irish.
All possible mutated forms are displayed for convenience.

^ “tobann”, in Historical Irish Corpus, 1600–1926, Royal Irish Academy
^ Gregory Toner, Sharon Arbuthnot, Máire Ní Mhaonaigh, Marie-Luise Theuerkauf, Dagmar Wodtko, editors (2019), “opunn”, in eDIL: Electronic Dictionary of the Irish Language
^ MacBain, Alexander; Mackay, Eneas (1911), “tobann”, in An Etymological Dictionary of the Gaelic Language‎^[1], Stirling, →ISBN, page 265
^ Quiggin, E. C. (1906), A Dialect of Donegal, Cambridge University Press, § 129, page 50