ess-

From Proto-Celtic *exs-, from Proto-Indo-European *h₁eǵʰs (“out”).

ess- (pretonic as-)

1. ex-, out

   ‎ess- (“out”) + ‎beirid (“to bring, carry”) → ‎as·beir (“to say”, literally “bring out”)

   ‎ess- (“out”) + ‎renaid (“to sell”) → ‎as·ren (“pay (off)”, literally “sell out”)

   ‎ess- (“out”) + ‎éirge (“rising”) → ‎esséirge (“resurrection”, literally “rising out”)

2. privative prefix: non-, dis-

   ‎ess- (“non-”) + ‎carae (“friend”) → ‎escarae (“enemy”, literally “non-friend”)

   ‎ess- (“non-”) + ‎báe (“benefit, utility”) → ‎esbae (“uselessness”)

   ‎ess- (“-less”) + ‎recht (“law”) → ‎eisrecht (“outlaw”, literally “lawless, i.e. not protected under the law”)

   ‎ess- (“-less”) + ‎tol (“desire”) → ‎etal (“pure, sinless”, literally “without desire”)

Originally, ess- manifested in the following distribution in stressed syllables:

• ess- proper before vowels and s-
• é- before resonants
• e- before stops, blocking lenition

Already in Old Irish, however, ess- proper can be seen encroaching on the environments of its other allomorphs.

• Irish: eas-
• Scottish Gaelic: eas-

• Gregory Toner, Sharon Arbuthnot, Máire Ní Mhaonaigh, Marie-Luise Theuerkauf, Dagmar Wodtko, editors (2019), “ess-, es-, e-, é-”, in eDIL: Electronic Dictionary of the Irish Language
• Thurneysen, Rudolf (1940) D. A. Binchy and Osborn Bergin, transl., A Grammar of Old Irish, Dublin Institute for Advanced Studies, →ISBN, § 834; reprinted 2017