trigeiniau

Welsh

trigain (“three score”, “sixty”) +‎ -iau

(North Wales, standard) IPA^(key): /trɪˈɡei̯njaɨ̯/
- (North Wales, colloquial) IPA^(key): /trɪˈɡei̯njɛ/, /trɪˈɡei̯nja/
(South Wales, standard) IPA^(key): /trɪˈɡei̯njai̯/
- (South Wales, colloquial) IPA^(key): /trɪˈɡei̯njɛ/

trigeiniau pl

(plural only) sixties (decade)
- 1972, Evan David Jones, “Cymru: oes Victoria ac Edward VII o hen ffotograffau”, in Victorian and Edwardian Wales from old photographs‎^[1], Batsford, →ISBN, page 11:
  Wedi i henaint oddiwes John Thomas, ac yntau’n awyddus i beidio â chwalu ei gasgliad, gwerthodd yr Oriel i Syr Owen Edwards, gan sicrhau cyfanrwydd casgliad gwych o fwy na thair mil о negatifau gwydr yn dyddio o’r trigeiniau i’r naw degau.
  (please add an English translation of this quotation)

Welsh mutation
radical	soft	nasal	aspirate
trigeiniau	drigeiniau	nhrigeiniau	thrigeiniau
Note: Some of these forms may be hypothetical. Not every possible mutated form of every word actually occurs.