Morphology: tre+tomen
Phonetic: tread-ohm-enn
The word "tre" can mean town or farm/homestead and here it is the latter meaning as farms called tredomanvach and Tredoman Vaur were recorded in 1783. The name had become Tretommen by 1813. The word "tomen" has many meanings depending on the context. One meaning is a "mound" and it is possible that it is a reference to a "mound of rocks", namely the Tredomen Rocks that can be seen from the A472 Ystrad Mynach to Nelson road. The name therefore probably means "farm near the mound of rocks".