The Collaborative International Dictionary of English v.0.48:

Monolithic \Mon`o*lith"ic\, a.
   Of or pertaining to a monolith; consisting of a single stone.
   [1913 Webster]

WordNet (r) 3.0 (2006):

monolithic
    adj 1: imposing in size or bulk or solidity; "massive oak
           doors"; "Moore's massive sculptures"; "the monolithic
           proportions of Stalinist architecture"; "a monumental
           scale" [syn: massive, monolithic, monumental]
    2: characterized by massiveness and rigidity and total
       uniformity; "a monolithic society"; "a monolithic worldwide
       movement"

Moby Thesaurus II by Grady Ward, 1.0:

109 Moby Thesaurus words for "monolithic":
   accordant, alike, austere, automatic, balanced, bare, basic,
   characterless, chaste, colossal, consistent, consonant, constant,
   continuous, correspondent, craggy, crystal, crystalline,
   elementary, enormous, equable, equal, essential, even, featureless,
   flat, fundamental, giant, gigantic, gravelly, gritty, homely,
   homespun, homogeneous, huge, immovable, immutable, impenetrable,
   imposing, indivisible, inflexible, intractable, invariable,
   invulnerable, irreducible, lapideous, level, lithoid, lithoidal,
   massive, measured, mechanical, mere, methodic, monumental,
   of a piece, ordered, orderly, pebbled, pebbly, persistent, plain,
   porphyritic, primal, primary, pure, pure and simple, regular,
   rigid, robotlike, rock-ribbed, rock-strewn, rock-studded, rocklike,
   rocky, sandy, severe, shingled, shingly, simon-pure, simple,
   single, smooth, solid, spare, stable, stark, steadfast, steady,
   stolid, stonelike, stony, systematic, trachytic, unadorned,
   unbending, unbroken, unchangeable, unchanged, unchanging,
   uncluttered, undeviating, undifferenced, undifferentiated,
   undiversified, uniform, unruffled, unvaried, unvarying