Opposite words for diminutive:
voluminous, Himalayan, mammoth, cavernous, enormous, fat, big, overscale, heroic, cosmic, oversize, stupendous, substantial, great, plenteous, boundless, mountainous, titanic, gross, wide, large, liberal, ample, copious, considerable, bountiful, immeasurable, husky, monstrous, sizable, king-size, humongous, gargantuan, hefty, monolithic, biggish, adequate, infinite, goodly, tidy, thick, galactic, hulking, immense, plentiful, vast, huge, incalculable, grand, monumental, healthy, appreciable, abundant, broad, prodigious, sufficient, handsome, leviathan, gigantic, colossal, boxcar, jumbo, giant, pharaonic, outsize, bulky, brobdingnagian, staggering, enough, massive, herculean, cyclopean, whacking, largish, elephantine, generous, tremendous, Bunyanesque, whopping.
Usage samples:
  1. Twenty minutes later Henley entered the gate of Sam Pitman's diminutive farm- house.
    "Dixie Hart", Will N. Harben.
  2. Pomponazzi was a diminutive man, and was nicknamed " Peretto."
    "A Biographical Dictionary of Freethinkers of All Ages and Nations", Joseph Mazzini Wheeler.
  3. " I see one now," declared John, turning and staring at his diminutive friend.
    "The Go Ahead Boys and Simon's Mine", Ross Kay.
  4. A diminutive messenger boy, with a super- experienced countenance, had met them half way to the vestibule, and, with a saucy smile, held up an envelope to Mr. Swift's face.
    "A Republic Without a President and Other Stories", Herbert Ward.