‑edd and ‑oedd are added to nouns orig. of other declensions as follows:
‑eẟ in Ml. W., ‑oedd in Mn. W. are added to tir m. ‘land’ (an old neut. s-stem), pl. tiret (‑t ≡ ‑ẟ) b.b. 33, tireẟ r.b.b. 40 (beside tirion § 35 iii), Mn. W. tiroedd D.G. 436, 524; mynydd m. ‘mountain’ (< *moníi̯o‑), pl. mynyẟeẟ w.m. 250, b.t. 11, r.b.b. 40, Mn. mynyddoedd; dwfr m. ‘water’ (neut. o-stem), pl. dyfreẟ Ỻ.A. 54, 65, Mn. dyfroedd.
mynyẟeẟ having become mynyẟe in S. W. dialects (cf. eiste § 110 iv (3)), this was wrongly standardized as mynyddau by some recent writers, but the traditional lit. form mynyddoedd prevails. The same remark applies to blynyddoedd, now sometimes written blynyddau for dial. blynyẟe < *blynyẟeẟ. In the above words ‑oeẟ may be old as a N. W. form, the prevailing forms in Ml. W. being S. W.
‑oedd was added to cant m. ‘hundred’ (neut. o-stem), pl. cannoedd; nerth m. ‘strength’ (neut. o-stem); mil f. ‘thousand’; mur m. ‘wall’, pl. muroeẟ w.m. 191, muroedd g. 237, later muriau; llu m. ‘host’ (m. o-stem), pl. lluoeẟ r.m. 175, Mn. lluoedd; byd m. ‘world’ (m. u-stem), pl. bydoeẟ m.a. i 199, Mn. bydoedd; nifer m. ‘host’, pl. niveroeẟ w.m. 54, Mn. niferoedd; mis m. ‘month’, pl. misoedd; teyrnas f. ‘kingdom’, pl. tyrnassoeẟ w.m. 50, Mn. teyrnasoedd; tŵr m. ‘tower’ (< E. < Fr.), pl. tyroeẟ w.m. 191, tyreu do. 133, Mn. tyrau; iaith f. ‘language’, pl. ieithoeẟ w.m. 469, b.t. 4, Mn. ieithoedd; gw̯ledd f. ‘feast’, pl. gwleddoedd D.G. 524, gwleddau do. 8; gwisg f. ‘dress’, pl. gwisgoedd; oes f. ‘age’, pl. O. W. oisou (with ð added at some distance, see fac. b.s.ch. 2, for ‘deest’ according to Lindsay, EWS. 46), Ml. W. oessoeẟ Ỻ.A. 103, oesseu b.t. 15, 19, Mn. W. oesoedd, oesau; achoet (t ≡ ẟ) B.B. 53, Mn. achoedd, achau ‘lineage’ both in L.G.C. 213, sg. ach f.; dyfnderoedd ‘depths’, blinder-oedd, ‑au ‘troubles’.
iii. i̯o-stems. (1) The vowel is affected in the sg.; the pl. ends in ‑ydd, ‑oedd, ‑edd.
The Ar. nom. endings were m. sg. *‑(i)i̯os, pl. *‑(i)i̯ōs; neut. sg. *‑(i)i̯om, pl. *-(i)i̯ā. In Kelt. *-(i)i̯ōs gave place to *‑(i)i̯oi > *‑(i)i̯ī; this gave ‑yẟ or ‑oeẟ according to the accent; neut. *‑íi̯ā gave ‑eẟ; ‑eẟ in m. nouns is prob. for ‑oeẟ. Where neither sg. nor pl. had i before i̯, we had e.g. dyn ‘man’ and ‘*men’; then a new dynion for the latter § 121 i.
