Antonyms of myriad:
calculable, homogeneous, homogenous, monolithic, unmixed, unvaried, alike, identical, same, distinct, distinctive, individual, separate, alone, lone, only, sole, solitary, singular, unique, finite, limited, countable, enumerable, numberable.
Examples of usage:
  1. A little while longer I sat by John's side, catching the dim outline of his face, half uplifted, looking towards those myriad worlds, which we are taught to believe, and do believe, are not more precious in the Almighty sight than one living human soul.
    "John Halifax, Gentleman", Dinah Maria Mulock Craik.
  2. Very often the whole swift precipice shows as a myriad million inch- thick cubes of clearest glass or ice or solidified light, falling in an envelope of starry spangles.
    "The Niagara River", Archer Butler Hulbert.
  3. O myriad sweet voices of the rain!
    "Rose and Roof-Tree Poems", George Parsons Lathrop.