1Sain are a Welsh duet (the name is Welsh for "Unison"), Meinir Thomas (who composes their songs) and Caroline Hughes, also known as Mêbs (lead vocals). They hail from Bodffordd, Anglesey. The name "1Sain" was chosen "to convey the unity and close relationship between them in their life, career and music", according to the sleeve notes on their CD "Gwaed Yn Dewach Na Dwr" (Gwynfryn Cymunedol, GCCD 16).