English: sill
Welsh: silff ffenestr
Subject: Ystadau a Cadw
English definition: The lowest horizontal member of a timber window; also the projecting stone member on which the window sits. 
Welsh definition: Darn llorweddol isaf ffenestr bren; fe’i defnyddir yn ogystal am y darn o faen yr eistedda’r ffenestr arno.
Welsh context: Ffynhonnell: Taflen wybodaeth gyhoeddus Cyngor Gwynedd.