References
Delyth Prys, J.P.M. Jones, Owain Davies, Gruffudd Prys (2006) Y Termiadur: termau wedi'u safoni; standardised terminology (in Welsh), Cardiff: Awdurdod cymwysterau, cwricwlwm ac asesu Cymru (Qualifications curriculum & assessment authority for Wales), →ISBN, page 34 R. J. Thomas, G. A. Bevan, P. J. Donovan, A. Hawke et al., editors (1950–present), “asid”, in Geiriadur Prifysgol Cymru Online (in Welsh), University of Wales Centre for Advanced Welsh & Celtic Studies