Notes:
The farm was renamed, from its former English self-explanatory name, in recent decades, after the nearby Late Iron Age courtyard house settlement of Bosullow Trehyllys. The word in its present form resembles tre ‘farm, settlement’ + henlys ‘old ruin, but is in fact a corruption of crellas ‘courtyard houses’ (the ancient village being Bosullow Crellas in the 19th century.