iii. (1) In Brit. the nom.-acc. sg. neut. ending must in some cases have been *‑ū (instead of *‑u), cf. Lat. cornū, etc. (so sometimes in Skr., see Brugmann² II ii 144), as in *dakrū > W. deigr ‘tear’ (e.g. llawer deigɏr a wyleis i h.m. ii 129 ‘many a tear have I wept’, bob deigr Dat. vii 17 “πᾶν δάκρυον”). The pl. ending might be *‑ou̯a (< *‑uu̯ə) or ‑ū (< *‑uu̯ə contracted, § 63 vii (2)); deigr ‘tears’ from the latter is doubtful, though used by Gr.O. 50; the former gives the usual pl. dagrau § 76 iii (2). See also § 125 iii Note.
(2) cainc ‘branch’ may be a fem. u̯ā-stem, with nom. sg. in ‑ū, Thurneysen Gr. 182; thus cainc < *kaŋkū, pl. cangau, Ml. W. cag̃eu b.b. 48 < *káŋkou̯ās.
iv. The pl. ending ‑au does not affect a preceding vowel, see § 76 iii (2); ceg̃eu b.b. 47 is a scribal error as shown by cag̃eu 48.
n-stems.
§ 121. i. ‑i̯on and ‑on come from Brit. ‑i̯ones and ‑ones, pl. endings of n-stems.
The Brit. forms were *‑ǖ < *‑ō, pl. ‑ones, as in Brittones; but *‑i̯ǖ < ‑i̯ō, pl. ‑i̯ones, as in Verturiones, Gaul. Suessiones, seems to have predominated, as in Goidelic (Thurneysen Gr. 202). Hence the greater prevalence of ‑i̯on. in W. Borrowed words were of course declined like native, and Lat. latrōnes > Brit. *latrŏnes > W. lladron.
In Ar., nouns in ‑ō(n), ‑i̯ō(n), ‑ii̯ō(n) (loss of ‑n § 101 ii (4)) were (a) nomina agentis, frequently from adjectives with o‑, i̯o‑, ii̯o- stems; thus Gk. στράβων ‘squinter’: στραβός ‘squinting’; οὐρανίων ‘heavenly one’: οὐράνιος ‘heavenly’; (b) abstract nouns, as Lat. ratio. Thus the use of ‑ion in W., which is added to names of persons and instruments, and to abstract nouns, corresponds roughly to the original value of the suffix.
‑on goes back to Brit. in nouns in which the vowel is affected in the sg., § 125 iii; after ‑hai < *‑sagi̯ō, pl. ‑heion re-formed for *‑haeon < *‑sagi̯ones, and after ‑ydd, pl. ‑yddi̯on, re-formed for ‑yẟon < ‑íi̯ones, as in gweryddon § 110 ii (3). But in most cases it is a new addition in W., as in ymerodron, pl. of ymherawdr < Lat. imperātor. W. dyni̯on is also prob. an analogical formation, for Ir. duine implies *donii̯os, and Bret. and Corn. use tud, tus ‘people’ for the pl. The adj. *doni̯os and its pl. *doni̯ī would both give dyn, to which ‑i̯on was added to form the new pl.
ii. ‑i̯on is added to (1) many nouns denoting persons, as dyn ‘man’, pl. dynion; mab ‘boy, son’, pl. meibion, Ml. meibon § 35 ii (1), O. W. mepion § 70 ii (1); gwas ‘servant’, pl. gweision, Ml. gweisson w.m. 33; ŵyr ‘grandson’, pl. w͡yrion, Ml. wyron r.b.b. 49; gwastrawd ‘groom’, pl. gwastrodẏon w.m. 33; including derivatives in ‑(h)ai, ‑ydd, ‑og Ml. ‑awc, ‑or Ml. ‑awr, ‑ig, ‑awdr, as gwestai ‘guest’, pl. gwesteion Ỻ.A. 168; crydd, pl. cryddion,
