ONlwSG

brag m. [b̥ɾaɡ̊], gen. braig [b̥ɾɛɡ̊ʲ], ‘bang, crack, pop, clap, crash (onomatopeic); drip (onomatopeic); report (sound)’ (AFB^˄). MacLennan (1925) lists the senses of SG brag m. as both ‘burst, explosion’ and ‘boast’, citing EG braigim (braiġim). There is some confusion here: (1) EG braiġiḋ 

Braiġim is the 1st sing. present absolute of the verb braiġiḋ (the 3rd sing. form) ‘farts’, verbal noun broim(m) (SG braim m. ‘fart’) (for this verb, see O’Rahilly 1929, 64–66).

contains a (palatal) velar fricative /ɣ’/; (2) similarly the related SG bragh m. ‘burst, explosion’ (e.g. HSS 1828, Dwelly 1911) has a (non-palatal) velar fricative /ɣ/; while (3) SG brag m. ‘boast’ (e.g. Armstrong 1825; < Eng. brag) and SG brag m. ‘bang’ both contain a velar plosive /ɡ/.

MacBain (1911) derives SG brag ‘bang’ etc. from ON brak nt. ‘bang, crash, din, noise, commotion’ 

NO: ‘brak, ståk, styr’.

(so also McDonald 2009, 345), and the development is regular. MacBain associates the Gaelic word with Lewis, but it has been recorded in Harris, Benbecula, South Uist, Barra, Skye and Tiree (AFB^˄) as well as in Strathglass (Faclan bhon t-Sluagh^˄). Its earliest attestation is apparently in Nicolson’s Gaelic Proverbs (≈1881, 229: Is e am brag a nì an cruadhachadh ‘When the cracking begins the grain gets dried’).

Derivatives: SG brag vb ‘to bang’ etc. and the verbal nouns bragadaich f. and bragail f. ‘banging’ etc. occur.