ad montem Berrwin 1191, ymynyded Berwyn 1165 (late 13c.), o uerrwyn c. 1268 (early 14c), da Verwyn, ar Ferwyn fawr 15c., or Ferwyn c.1500, the Berwyn hills 1804-13, Cader Berwyn 1831-2, -, Berwyn 1838
Probably Welsh bar(r), 'head, summit', and gwyn, 'white, fair, pale' etc., perhaps a mountain with snow on it; local Welsh -speakers call it Y Berwyn with the de. art., also seen in some of the spellings above. The n. is now applied to the hills between Cymiau Nod (SH 9827 and Foel (SJ 1839) DNB but may once have referred specifically to Cadair Berwyn (SJ 072327). Welsh cadair, 'chair',, refers to the shape of the mountain, found also in Cadair/Cader Idris Merionethshire, 'chair of Idris'. The -a- of Bar- probably developed into Ber- under the influence (vowel affection') of the -y- in wyn. There is also a hill called Berwyn near to Llansanffraid-ym-Mechan (SJ2022).