English: cylinder glass
Welsh: gwydr silindr
Subject: Ystadau a Cadw
English definition: Sheet formed by blowing an elongated cylinder from molten glass, which is then cut along its length and laid flat, to cool, before being subdivided into smaller sheets. 
Welsh definition: Dalen a ffurfir drwy chwythu gwydr tawdd yn silindr hir, a dorrir ar ei hyd a’i wastatau a’i oeri, cyn ei dorri’n ddalennau llai.
Welsh context: Ffynhonnell: Taflen wybodaeth gyhoeddus Cyngor Gwynedd.