Antonyms of diminutive :
big, large, bulky, hefty, hulking, massive, voluminous, boxcar, brobdingnagian, Bunyanesque, cavernous, colossal, cyclopean, elephantine, enormous, galactic, gargantuan, giant, gigantic, gross, Himalayan, herculean, heroic, huge, humongous, immense, jumbo, leviathan, mammoth, monolithic, monstrous, monumental, mountainous, pharaonic, prodigious, staggering, stupendous, titanic, tremendous, vast, abundant, ample, appreciable, bountiful, copious, generous, healthy, liberal, plenteous, plentiful, fat, thick, broad, wide, boundless, cosmic, immeasurable, incalculable, infinite, adequate, enough, sufficient, biggish, considerable, goodly, grand, great, handsome, husky, king-size, largish, outsize, overscale, oversize, sizable, substantial, tidy, whacking, whopping.
Examples of usage:
Inwardly pleased at the way he had winked at her with no one else the wiser, Si'Wren bowed low, then rose to her full, diminutive stature and nodded to him in mute obedience. "Si'Wren of the Patriarchs", Roland Cheney.
I was always " Mashinke," or else " Mashke," by way of diminutive. "The Promised Land", Mary Antin.
Fortunately, I added, I had already received an offer to join one of the private parties who drive up, fourteen or fifteen persons behind one diminutive pony- and that, as he well knew, would be a matter of only a few pence. "Old Calabria", Norman Douglas.