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§ 145 pl. lleithron (lleithɏrẏon in . 7bi). The affection of the vowel in geirw̯on etc. bears witness to the lost i̯.

Some adjectives have two plurals, one formed by affection, and one by adding ‑i̯on: hardd ‘handsome’, pl. heirdd, heirddion; garw̯ ‘rough’, pl. geirw̯, geirw̯on; marw ‘dead’, pl. meirw̯, meirw̯on.

i. The only pl. forms which are originally adjectival are those produced by vowel affection; where these exist they generally accompany pl. nouns, thus gwŷr cedyrn, not gwŷr cadarn. But we have seen that from the Ar. period *‑i̯ō, pl. *‑i̯ones formed nouns corresponding to adjectives in *‑i̯os § 121 i; and there can be no doubt that W. forms in ‑i̯on (from *‑i̯ones) were originally nouns, as they may still be, e.g. y tlodion ‘the poor’. The distinction between these nouns and adjectives proper was obscured by the fact that adjectives might be used as nouns, e.g. y kedyrn 51 ‘the mighty’; then, in imitation of gwŷr cedyrn ‘mighty men’, expressions like plant tlodion ‘poor children’ were formed for the sake of formal agreement, as the agreement was not apparent in an adj. like tlawd which had the same form for sg. and pl. But the old tradition persisted, and the use of forms in ‑i̯on was, and is, optional: eriron du, …coch, eririon gwinn, …glas, …lluid 72–3 ‘black…, red…, white…, blue…, grey eagles’; dynyon mwyn  21 ‘gentle folk’, meirch dof do. 31 ‘tame horses’; and is more frequent in later than in earlier periods, thus bratteu trwm of 23 appears as bratteu trymẏon in the later  14. Hence we find (1) as forms in ‑i̯on were not really needed, many adjectives remained without them, and have no distinctive pl. forms; (2) in many cases plurals in ‑i̯on remain substantival.

The following adjectives have no distinctive plural forms in use: