ONlwSG

oglaidh adj. [ˈoɡ̊ɫ̪i] 

/ogLɪ/ (AFB^˄); [ogly] (MacLennan 1925).

and [ˈɔɡ̊ɫ̪i] 

M^cAlpine 1932: [ŏg´-lė].

‘volatile, changeable; unstable, unsteady; fearsome, wild; dismal, gloomy’ (AFB^˄), also ‘queasy’ (pers. comm. Ailig Dòmhnallach, Skye). McDonald (2009 

Citing SG ogluidh, the older spelling.

) notes MacBain’s derivation (1896, 1911, s.v. ogluidh) from ON uggligr ‘to be feared’ and reference to Eng. ugly (1911), and considers the derivation likely. Occasional overlap between /o/ and /u/ is found in some Scottish Gaelic dialects, e.g. in (Leurbost) coimhead, ochd, tunnag and uchd (Oftedal 1956, 72–73), 

Cf. also SG *seòrr/teòrr > siùrr/tiùrr, s.v. tiùrr.

and therefore a derivation from either ON ugglig acc. or Scots o(u)gly, oogly [ˈugli] (SND^˄) 

Or perhaps modern Eng. ugly /ˈʌɡli/ (OED^˄). (Eng. ugly and Scots o(u)gly etc. are themselves from Old Norse ugglig.)

is at first sight plausible. However, compare EG ocal adj. ‘?quick to take offence, touchy, passing into that of irascible, hot-tempered’ and ocla adj. ‘readily incensed, irritable, imperious’ (eDIL^˄), 

eDIL^˄ suggests ocla adj. may arise from the genitive singular of ocla f. ‘hasty or imperious disposition, quick temper’, itself from ocal adj.

so modern Ir. ogal adj. ‘hasty, angry, dangerous, obstinate; fearful’ and ogla f. ‘obstinacy, fearsomeness’ (Dinneen 1947). In the main, the senses of SG oglaidh suggest the word derives from EG ocal or ocla + the adjectival suffix -(a)idh, 

The suffix -(a)idh is a metathesised form of the Early Gaelic adjectival suffix -ḋ(a)e (Thurneysen 1975, 220–21), e.g. EG neṁḋae > SG nèamhaidh ‘heavenly’ (Calder 1972, 183; Cox 1917, 151).

although it may have acquired some of its senses from Scots o(u)gly etc. or Eng. ugly.

O’Reilly (1864) gives Ir. ogluidh (which Dinneen cites as oglaidhe) ‘bashful, fearful, awestruck’ and ogluidheachd f. ‘bashfulness, fear, awe’, but these are likely to have been adopted from Shaw 1780: SG ogluidh ‘bashful, afraid, awestruck’, ogluidhachd (sic) ‘bashfulness, awe, fear’.

Derivatives: an abstract noun in -achd occurs in the form oglachd in Alasdair Mac Mhaighstir Alasdair’s ‘Birlinn Chlann Raghnaill’ (Thomson 1996b, 149, l. 1833; c. 1750, ibid. 137) and Mac Coinnich’s Eachdraidh na h-Alba (1867, 94); in the form ogluichd in Leabhar nah‘Urnuigh Choitchionn (1794, 315); but more frequently and generally more recently as ogluidheachd, now oglaidheachd.