iv. A noun with a pl. ending sometimes has its vowels affected as an additional sign of the pl., as ceraint for carant § 123 v, adenyẟ for adaneẟ § 125 iii, brodyr for broder § 124 i, which are therefore, in a sense, double plurals.
Plural Doublets.
§ 129. i. A noun not ending in ‑yn or ‑en may have more than one pl. form in the following ways:
(1) One pl. may be formed by affection and one by the addition of an ending: môr ‘sea’, pl. mŷr, moroeẟ § 122 ii (4); arf ‘weapon’, pl. arveu w.m. 97, 99, etc., poet, eirf D.G. 2; esgob ‘bishop’, pl. esgyb, later esgobion (15th cent, Gnt.O. a 14967/87), esgobiaid (T.A. a 14975/61), the first and last now obsolete; Ml.W. kévɏnderw̯ ‘cousin’, pl. kévɏndɥru, a.l. i 222, Mn. W. cefnder, pl. cefndyr, cefnderoedd L.G.C. 167.
In Recent Welsh new and inelegant weak forms are sometimes found, as castelli, alarchod for cestyll, elyrch. On the other hand in the late period we meet with spurious strong forms, such as edyn § 125 iii Note; and latterly emrynt for amrannau (amrantau) § 120 i (1); brieill for briallu § 134 ii; creig for creigiau.
(2) Two or more plurals may be formed by adding different endings: tref ‘town’, pl. trefi, trefydd § 122 ii (2); kaer ‘castle’, pl. keyrydd, kaeroedd, caereu, do. (3); achau, achoedd L.G.C. 213 ‘ancestry’; dyn § 127, etc. See § 131 i.
(3) Two plurals with the same ending may have different vowel changes; thus Ml. W. ceing old pl. cangeu § 125 iii, newer pl. ceingheu Ỻ.A. 144; these survive in Mn. W. as cainc pl. cangau, ceinciau. So cawr ‘giant’, pl. ceuri, cewri § 76 iv (3); achaws, achos ‘cause’ pl. achwysson § 125 v (3), achuysẏon a.l. i 30, and achosion.
ii. A noun ending in ‑yn or ‑en may have more than one pl. form as follows:
(1) Some nouns of class 1, § 126 i, have two plurals, one without and one with the vowel affected; as gwïalen ‘twig’, pl. gwḯal or gwḯail; seren ‘star’, pl. sêr b.t. 26, or sɥ̂r Ỻ.A. 5, the latter now obsolete; collen ‘hazel’, pl. coll m.m. 32, generally cɥll; onnen ‘ash’, pl. onn, more usually ɥnn; mellten ‘flash of lightning’, pl. mellt Ỻ.A. 107, rarely mɥllt r.b.b. 259.
