On the first edition of the 25 inch OS maps, published in 1889, the farm was named 'Bryn-y-garth-uchaf,' meaning 'the hill of the upper promontory' or 'the hill of the upper enclosure.' However, by the time the second edition was published in 1901, the name of the farm had changed to 'Bryn-y-gath,' meaning 'hill of the cat.' Bryn-y-gath farm is situated about four and a half miles south east of Trawsfynydd.
Additional source: glossary of Welsh Place names - https://historicplacenames.rcahmw.gov.uk/glossary
M. Ryder, RCAHMW, 3rd October 2018.