Same word as uncompounded:

Spartan, absolute, austere, classic, clean, discreet, elementary, folksy, homely, homey, humble, inelaborate, lowly, mere, modest, not complex, open and shut, plain, pure, pure and simple, rustic, sheer, single, unadorned, unadulterated, unaffected, unalloyed, unblended, uncombined, uncomplicated, uncompounded, undecorated, unelaborate, unembellished, unfussy, unmitigated, unmixed, unornamented, unostentatious, unpretentious, unqualified, vanilla