-iaeth

• -aeth

From Proto-Brythonic *-aɨθ, from Insular Celtic *-axtā, suffixal use of Proto-Celtic *axtā. Cognate with Cornish -ieth.

• (North Wales, standard, colloquial) IPA^(key): /jaɨ̯θ/
  • (North Wales, colloquial) IPA^(key): /jɛθ/, /jaθ/
• (South Wales, standard) IPA^(key): /jai̯θ/
  • (South Wales, colloquial) IPA^(key): /jɛθ/

-iaeth f (plural -iaethau)

1. Forms abstract nouns.

   ‎arwr (“hero”) + ‎-iaeth → ‎arwriaeth (“heroism”)

   ‎deintydd (“dentist”) + ‎-iaeth → ‎deintyddiaeth (“dentistry”)

   ‎cydnabod (“recognise, acknowledge”) + ‎-iaeth → ‎cydnabyddiaeth (“recognition, acknowledgement”)

   ‎llaw (“hand”) + ‎trin (“to treat”) + ‎-iaeth → ‎llawdriniaeth (“surgery”)

2. territory controlled by, -ship, -age, -y, -dom

   ‎barwn (“baron”) + ‎-iaeth → ‎barwniaeth (“baronage, barony”)

• With names of leaders, -iaeth can be both concrete and abstract, for instance barwniaeth (“baronage, barony”) is both the rank of being a baron and the territory controlled by one.

• Most nouns in -iaeth are feminine. Common exceptions are gwahaniaeth (“difference”) and lluniaeth (“refreshments”).

R. J. Thomas, G. A. Bevan, P. J. Donovan, A. Hawke et al., editors (1950–present), “-iaeth”, in Geiriadur Prifysgol Cymru Online (in Welsh), University of Wales Centre for Advanced Welsh & Celtic Studies