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Definition: Gyrru pyst blaenllym pren neu fetel i waelod afon, môr etc i gynnal seiliau uwchstrwythur
Context: Er mwyn rhoi sylw i hyn, mae Gweinyddiaethau’r DU wedi sefydlu Cofrestrfa Synau Morol ar gyfer cofnodi synau ergydiol fel y rheini a gynhyrchir wrth osod seilbyst neu gynnal arolygon seismig.