English: sealed unit
Welsh: uned wedi ei selio
Subject: Ystadau a Cadw
English definition: Double glazing in which air is withdrawn from the space between two sheets of glass to form a vacuum, and the edges sealed. 
Welsh definition: Gwydr dwbl gyda’r aer wedi ei dynnu o’r gwagle rhwng y ddwy ddalen o wydr i ffurfio faciwm, a’r ymylon wedi eu selio.
Welsh context: Ffynhonnell: Taflen wybodaeth gyhoeddus Cyngor Gwynedd.