Henllys means 'ancient court' with hen 'ancient' and llys 'court'.
The name may refer to the former administrative court of the lordship of Machen http://www.ccgc.gov.uk/landscape--wildlife/protecting-our-landscape/special-landscapes--sites/protected-landscapes-and-sites/sssis/sssi-sites/henllys-bog.aspx Today Henllys is a residential area and community on the edge of Cwmbrân in South East Wales,http://historypoints.org/index.php?page=cwrt-henllys-hotel-cwmbran   with a population of 2,682 as of the 2011 census.https://www.nomisweb.co.uk/reports/localarea?compare=W04000764 See also
Cwmbran
Torfaen County Borough Council
Grade II* listed buildings in Torfaen
Scheduled Monuments in Torfaen
Communities of Torfaen
References
