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From Middle Welsh dyð, from Old Welsh did, from Proto-Brythonic *dið, from Proto-Celtic *dīyos (compare Cornish dydh, Breton deiz, Old Irish día), from Proto-Indo-European *dyḗws (compare Latin diēs).





dydd m (plural dyddiau)

  1. day, daytime

Usage notes

  • Dydd generally refers to the uncountable period of light. Dydd is also used with the names days of the week and with holiday and festival names. It its in contrast to the word nos (night, evening). (cf. French jour, Italian giorno)
yn ystod y dyddduring the day(time)
dydd WenerFriday day(time)
Dydd CalanNew Year's Day
  • Diwrnod, on the other hand, is countable and refers to an individual day and so is the word used when employing a qualifying numeral or adjective. It is there the opposite of noson (night, evening). (cf. French journée, Italian giornata)
diwrnod gwycha great day
tri diwrnodthree days

Derived terms



Welsh mutation
radical soft nasal aspirate
dydd ddydd nydd unchanged
Note: Some of these forms may be hypothetical. Not every possible mutated form of every word actually occurs.


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