simple
1 clear, easy, easy-peasy (slang) elementary, intelligible, lucid, manageable, plain, straightforward, uncomplicated, understandable, uninvolved
2 classic, clean, natural, plain, severe, Spartan, unadorned, uncluttered, unembellished, unfussy
3 elementary, pure, single, unalloyed, unblended, uncombined, undivided, unmixed
4 artless, childlike, frank, green, guileless, ingenuous, innocent, naive, natural, simplistic, sincere, unaffected, unpretentious, unsophisticated
5 bald, basic, direct, frank, honest, naked, plain, sincere, stark, undeniable, unvarnished
6 homely, humble, lowly, modest, rustic, unpretentious
7 brainless, credulous, dense, dumb (informal) feeble, feeble-minded, foolish, half-witted, moronic, obtuse, shallow, silly, slow, stupid, thick
Antonyms
1 advanced, complex, complicated, convoluted, difficult, elaborate, highly developed, intricate, involved, refined, sophisticated
2 contrived, elaborate, fussy, intricate, ornate
4 artful, smart, sophisticated, worldly, worldly-wise
6 extravagant, fancy, flashy
7 astute, bright, clever, intelligent, knowing, on the ball, quick, quick on the uptake, quick-witted, sharp, smart, wise
simple-minded
1 a bit lacking (informal) addle-brained, backward, brainless, dead from the neck up (informal) dim-witted, feeble-minded, foolish, idiot, idiotic, moronic, retarded, simple, stupid
2 artless, natural, unsophisticated