gwrthdoriad

== Welsh == === Etymology === gwrthdorri (“to refract”) +‎ -iad. === Noun === gwrthdoriad m (plural gwrthdoriadau) (physics) refraction Synonyms: plygiad, gwyrdroad === Further reading === D. G. Lewis, N. Lewis, editors (2005–present), “gwrthdoriad”, in Gweiadur: the Welsh–English Dictionary, Gwerin R. J. Thomas, G. A. Bevan, P. J. Donovan, A. Hawke, et al., editors (1950–present), “gwrthdoriad”, in Geiriadur Prifysgol Cymru Online (in Welsh), University of Wales Centre for Advanced Welsh & Celtic Studies