Tyddyn Felin is a farm situated about a mile north east of Trawsfynydd. On the first and second editions of the OS 25 inch maps (published in 1889 and 1901 respectively), the farm is called 'Tyddyn-y-felin-isaf,' which translated as 'Lower-mill-house.' About a third of a mile to the south east there is a 'Tyddyn-y-felin-uchaf,' meaning 'Upper-mill-house' recorded on these maps. Tyddyn-y-Felin Uchaf is not recorded on modern maps, indicating that perhaps that farm no longer exists, and so there is no longer any need to distinguish between 'Uchaf' and 'Isaf.'
M. Ryder, RCAHMW, 4th October 2018.