Lat. pruīna < *prusuīna;—W. trew ‘sneeze’ < *(s)treu‑s‑, √pstereu- § 96 ii (4);—W. blew ‘hair’ < *bleus- § 101 iii (2).
The reason seems to be that *eus became *ehu̯ before the degradation of the first element of the diphthong.
(3) The diphthong was liable to be simplified by dissimilation when the following syllable contained u̯ or u; thus Ar. *tauros ‘bull’ became Kelt. *tauru̯os (in imitation of *u̯eru̯ā > Ml. Ir. ferb ‘cow’, Vendryes MSL. xii. 40), whence Kelt. *taru̯os > Ir. tarb, W. tarw ‘bull’. Later, when au had become ou in Brit., *ou-tūt- > *o-tūt- > W. odid ‘rarity’, beside Ir. ōthad, uathad < *au-tāt‑, both from *pau‑: Lat. pau-cu‑s, O.H.G. fōh, E. few.
iii. (1) Before a vowel the diphthong became aw when unaffected. Thus W. naw ‘nine’ < Brit. *nou̯an < Ar. *neu̯n̥;—W. baw ‘dirt’ < *bou̯‑, beside budr ‘dirty’ < *bou-tro- √peu̯(āˣ)‑: Lat. pūs, etc. § 101 iii (2);—W. awydd ‘desire’ for *aw̯w͡yẟ (rh. with rhŵyẟ § 38 x) < *au̯eid‑: Lat. avidus < *au̯id‑, √au̯ei̯‑.—So Brit. au for unacc. āu as in Ml. W. andaw ‘listen’, met. for *adnaw < *áti-gnā-u- ‘attend to’ < *g̑n̥̄‑u̯- √g̑enē‑: Lat. nāvus, Ir. aithgne ‘cognitio’. So also uu̯ for Lat. u before a vowel, as W. cystrawen ‘syntax’ < Lat. construenda.
(2) But in the penult (the present ult.) post-tonic ´‑ou- gives Ml. W. ‑eu, Mn. W. ‑au; thus the pl. endings *´‑ou̯es, *´‑ou̯a give W. ‑eu, ‑au, as in cadau ‘armies’ < *kátou̯es, dagrau ‘tears’ < Ar. *dák̑ruu̯ə; similarly angau ‘death’ < *ánkou̯‑; cigleu ‘I have heard’ < *k̑ū́k̑lou̯a § 182 i.
In this case ‑eu does not affect a preceding a as it does when it is itself the result of affection § 69 vi, as in teneu < *tanouís.
The above change may be due to a doubling of u̯, see § 62 i (2), thus *auu̯ > *üu̯ > *üü̯ > *öü > O. W. oü, Ml. W. eü.
(3) i̯ou̯- gives W. ieu (≡ i̯eü). Thus W. ieuanc ‘young’ < Brit. *i̯ou̯ankos < Ar. i̯uu̯n̥k̑os: Lat. juvencus § 100 i (1);—W. Ieuan < *I̯ou̯ánnes for lōánnes;—Mn. W. Iau, Ml. W. Ieu ‘Jove’ < Brit. gen. *I̯ou̯-os for Lat. Jovis;—Mn. W. iau, Ml. W. ieu ‘yoke’ < *i̯ou̯-ón < *juɡ-óm, see vi (1). Here we have the assimilation of u̯ to i̯ by which it becomes ü; cf. the assim. of i̯ to ü in ‑i̯oü in O. W., § 25 i.
An alternative form i̯ef‑, if- appears in the penult: iefanc, ifanc; Iefan, Ifan. The latter is attested in the 14th cent: ivanghet c.m. 84. Later it is common: Pawb yn eu rhif yn ifanc S.C., c. i 114 ‘all in their [full] number young’.
