riobh f. occurs along with the article in the Lewis village name An Riobh [ə ˈɍɪf], [ə ˈɍɯ̟f],
Cf. nMO: [ʀɪf], [ʀɯf].
gen. Na Riobhadh [nə ˈɍɪvəɣ], [nə ˈɍɯ̟vəɣ], NB108345. Citing the anglicised form of the place-name, Reef, Oftedal (1954, 387) suggests that it derives from ON *Rif nt. ‘(marine) reef’. However, there is no reef in the vicinity, and it is more likely that SG riobh derives from ON rifa f. ‘rent, rift’, the very feature found at the north end of the settlement. Furthermore, the presence of the Gaelic article suggests that we are probably dealing with a Norse loan-word rather than loan-name, albeit one that is no longer current in the lexicon. ON rifa would yield EG *[ˈɍiβə] in the first instance. For apocope, cf. Am Bac, with a loan-word from ON bakka, acc. of ON bakki m. (s.v. bac);
While apocope in the form of a caducous schwa (cf. Oftedal 1956, 149–50) is commonest after historically voiceless consonants, it can also occur after historically voiced consonants, e.g. Seachd ròin, sàth muice-mara big’ [for bige], | Seachd mucan-mara beaga, sàth muice-mara móire ‘Seven seals, a full meal for a small whale, | Seven small whales, a full meal for a big whale’ (Campbell 1978, 149.794).
for devoicing of the voiced fricative before pausa, but its retention in the genitive case, cf. A’ Chlibh, gen. Na Clibheadh (s.v. clibh).