just,
only, merely, purely, basically, solely
plainly,
minimally, cleanly, austerely, unpretentiously
antonym: elaborately
modestly,
humbly, unassumingly, meekly, unpretentiously, artlessly
antonym: proudly
easily,
straightforwardly, in basic terms, in simple terms, in words of one syllable,
crudely
antonym: elaborately
naively,
guilelessly, ingenuously, candidly, innocently, naturally
antonym: knowingly
frankly,
absolutely, obviously, undeniably, unquestionably, easily