For Tiree, Holliday (2021, 654) gives the form urdha [ˈurəˌɣɑ] (sic).
gen. idem, ‘a pile of boulders’ is derived from ON urð f. ‘idem’ by Oftedal (e.g. 1980, 177) and Cox (e.g. 1991, 492; 1992, 138); McDonald (2009, 424–25) considers the loan likely. The Gaelic word is obsolete but attested in place-names: (sing.) SG An Turdha (< *An t-Urdha) or Urdha Chràignis NL925457 (Tiree) (Holliday 2021, 654); (plur.) SG Na h-Urrdhannan [nə ˈhuɍ͡uɣəᵰ̪ən] NB233454 (Cox 2002a, 390), Urrannan Béaga NB357444 (OS 1843–82; cf. [nə ˈhʊʀʊ̀ɴən] (nMO)) and *Na h-Urrdhaichean [nə ˈh[UṚU]`içən] (Bernera) (Borgstrøm 1940, 213) (all in Lewis); and (with the Gaelic, nominally diminutive suffix -ag used as a collective) SG An Urrdhag [ə ˈᵰ̪uɍ͡uɣaɡ̊] NB197439 (Cox ibid.), Urraghag NB185440, Loch Urraghag ‘the loch of—’ NB321478 (OS 1843–82) (both in Lewis), and (plural) *Na h-Urrdhagan [nə ˈh[uRu]ɣɑkən] (Harris) (Borgstrøm ibid.); also SG Cnoc an Urrdhaig, a development from *Cnocan Urrdhaig ‘the hillock of—’, NB2546 (Lewis) (Cox ibid., 54, 221).
Gordon (1963, 107) lists Carn Urugag [ˈ[vʀv]ɣak‘] [sic] in Skye, but we should probably read SG Càrn Urrdhaig -[ˈuɍ͡uɣæɡ̊ʲ] ‘the cairn of—’, with genitive of the specific.
,
Taylor (2011, s.v. Urgha) gives the sense of SG Urgha in Harris as ‘rubble mound’. The Gaelic form in this instance is probably a loan-name from ON *Urða, a feminine derivative with the sense ‘(the) stony one, (the) stony river’ (cf. Cox 2022, 79–90).
Evidently, ON urð was borrowed into Gaelic after the falling together of /ð/ with /ɣ/
‘The earliest examples of this [development] are found (for palatalised δ) about the end of the eleventh century, and the fusion must have been complete by the thirteenth’ (Thurneysen 1975, 77; see also O’Rahilly 1926b, esp. 163–64 and 193–95; 1976, 65; Ó Maolalaigh 2006a, 42; 2008, 231–33).
and the development of stressed epenthesis (svarabhakti)
O’Rahilly 1976, 199–202.
in Gaelic; contrast ON *Garðabólstað acc. ‘(the) farm of the enclosures’ > SG Garrabost [ˈɡ̊ɑɍə ̩b̥ɔs̪t̪], with assimilation of the dental but absence of epenthesis (s.v. gàrradh). (For discussion of the develpment of ON rð in Gaelic, see Cox 2007b.)