gwactod

== Welsh == === Etymology === From gwag ("empty") + dod. === Pronunciation === IPA(key): /ˈɡwaktɔd/ === Noun === gwactod m (uncountable) (physics) vacuum === Mutation === === References === R. J. Thomas, G. A. Bevan, P. J. Donovan, A. Hawke, et al., editors (1950–present), “gwactod”, in Geiriadur Prifysgol Cymru Online (in Welsh), University of Wales Centre for Advanced Welsh & Celtic Studies