Modern Welsh coinage, composed of the vocabulary words glân ‘clean, pure, holy’ + da ‘good’. It is also used outside Wales, and is associated particularly with the actress and politician Glenda Jackson (b. 1937).
Scottish: Anglicized form of Gaelic Mac Cionaodha or Mac Cionaoith ‘son of Cionaodh’, a personal name which is probably composed of the elements cion ‘respect’, ‘affection’ + Aodh, a Gaelic personal name, originally the name of the Celtic god of fire. The personal name thus probably means ‘beloved of Aodh’.