Sounding like thunder.

Roget 192: large, big; great etc. (in quantity) 31; considerable, bulky, voluminous, ample, massive, massy; capacious, comprehensive; spacious etc. 180; mighty, towering, fine, magnificent.    corpulent, stout, fat, obese, plump, squab, full, lusty, strapping, bouncing; portly, burly, well-fed, full-grown; corn fed, gram fed; stalwart, brawny, fleshy; goodly; in good case, in good condition; in condition; chopping, jolly; chub faced, chubby faced.    lubberly, hulky, unwieldy, lumpish, gaunt, spanking, whacking, whopping, walloping, thumping, thundering, hulking; overgrown; puffy etc. (swollen) 194.    huge, immense, enormous, mighty; vast, vasty; amplitudinous, stupendous; monster, monstrous, humongous, monumental; elephantine, jumbo, mammoth; gigantic, gigantean, giant, giant like, titanic; prodigious, colossal, Cyclopean, Brobdingnagian, Bunyanesque, Herculean, Gargantuan; infinite etc. 105.    large as life; plump as a dumpling, plump as a partridge; fat as a pig, fat as a quail, fat as butter, fat as brawn, fat as bacon.    immeasurable, unfathomable, unplumbed; inconceivable, unimaginable, unheard-of.    of cosmic proportions; of epic proportions, the mother of all, teh granddaddy of all.    ... show more

Roget 404: loud, sonorous; high-sounding, big-sounding; deep, full, powerful, noisy, blatant, clangorous, multisonous^†; thundering, deafening etc. v.; trumpet-tongued; ear-splitting, ear-rending, ear-deafening; piercing; obstreperous, rackety, uproarious; enough to wake the dead, enough to wake seven sleepers.    shrill etc. 410 clamorous etc. (vociferous) 411 stentorian, stentorophonic^†.    ... show more

Extraordinarily big or impressive.