1 merely, barely, purely, only, solely, just, entirely, fully, totally, wholly, altogether, absolutely, really:
Is it true that they met regularly simply to discuss politics?
2 totally, completely, altogether, entirely, just, plainly, obviously, really, unreservedly, unqualifiedly:
If you believe that, you're simply too stupid for words!
3 naïvely, artlessly, guilelessly, openly, innocently, ingenuously, unaffectedly, unpretentiously, plainly, naturally:
He asked her very simply what she did as a 'working girl'.
4 plainly, modestly, starkly, severely, sparely, sparsely, austerely, ascetically:
His home is simply furnished, without paintings or any other decoration.
5 distinctly, unambiguously, plainly, obviously, unmistakably or unmistakeably:
The instructions must be written simply so that they are understandable to anyone.