ONlwSG

ùdail adj. [ˈuːd̪̥al] ‘inhospitable, churlish’ and ùdlaidh adj. [ˈuːd̪̥ɫ̪i] ‘gloomy’ are compared with ON útlagi m. ‘outlaw’ and útlegð 

Not útlagð as MacBain (1896; 1911) has it.

f. ‘outlawry’ – ON útlagi, if not MEng. ūtlagha, ūtlaghe, already gives EG útluighe ‘outlaw, miscreant’ (eDIL^˄) – but on semantic grounds McDonald (2009, 425) considers the link uncertain. A number of related forms are detailed below:

A. SG udail, ùdail noun and adj.
A 1. SG udail, ùdail m. [ˈu(ː)d̪̥al]
(i) udail (M^cAlpine 1832: [ŭd´-al] ‘churl’);
(ii) ùdail (HSS 1828: ‘gloomy, churlish or peevish fellow’).

A 2. SG udail, ùdail adj. [ˈu(ː)d̪̥al]
(i) udail (Shaw 1780: ‘inhospitable’; M^cAlpine 1832: [ŭd´-al] ‘gloomy’; Dwelly 1911: ‘inhospitable, gloomy’);
(ii) ùdail (HSS 1828: ‘inhospitable, churlish’).

B. SG udlaidh, ùdlaidh adj. [ˈu(ː)d̪̥ɫ̪i]
(i) udlaidh (MacFarlane 1825: ‘morose, lonely, churlish, gloomy’; Armstrong 1825: ‘lonely, morose, churlish, gloomy’);
(ii) ùdlaidh (HSS 1828: ‘gloomy, dark’; MacLennan 1925: ‘dark, gloomy’; Dwelly 1911: ‘gloomy, dark, churlish, morose, unsociable, lonely’; AFB^˄: /uːdLɪ/ ‘inhospitable, unsociable; dark, gloomy’, Skye, Wester Ross).

C. SG ùdlachd f. [ˈuːd̪̥ɫ̪əxk], -[axk, -[ɔxk]
In MacLennan 1925: ‘gloom’.

Forms A–C conceivably go back to Scots ool(e)d, oolt ‘downtrodden, downcast, cowed, nervous, subdued, bewildered, dumbfounded’ (past participle of ool ‘to treat harshly, ill-use, bully, wreck the health or spirits of; to be dejected and subdued, as from illness’) (SND^˄), cf. also Scots oolet in the sense ‘a disgruntled, peevish, dismal person or child’ (ibid.): 

SND^˄ gives ool sbs. and vb [uːl] and oolet (without pronunciation), which is compared with hoolet [ˈhulɪt]; The Online Scots Dictionary^˄ gives oul sbs. and vb [ul], oulet [ˈulɪt] and hoolet [ˈulɪt]; assuming the words are connected, cf. (Shetland) ul vb [ūl] and ulet [ūlet] (Jakobsen 1928, s.vv. ²ul, ¹ulet).

Scots oold (perhaps via SG *ulda ~ *ùlda) yields SG udail ~ ùdail m. (A 1), with metathesis, 

Perhaps cf. the adjectival formations SG dùldaidh > dùdlaidh ‘dark, gloomy’ (the direction of travel according to Calder (1972, 18, s.v. dùdlachd)); also EG attluġuḋ > SG altachadh ‘grace, blessing’, EG rétla > rélta, rélla > SG reul ‘star’ and EG utlach > ultach > SG ultach ‘armful etc.’.

also used adjectively (A 2), while, with the addition of the suffix -aidh on the one hand and the suffix -achd on the other, udail ~ ùdail yields the adjective udlaidh ~ ùdlaidh 

With -aidh, a metathesised form of EG -ḋae (Cox 2017, 151).

and the abstract noun ùdlachd, respectively. For variation in the length of the stressed vowel, cf. SG udabac ~ ùdabac (s.v.) and udrathad ~ ùdrathad (s.v.).