(The above illustration doesn't really relate to the subject of today's post, fellow babies... but I couldn't find anything that was more appropriate! Sorry!)
I hate it when people use the word "supposably" when they mean "supposedly." And yes, unfortunately, "supposably" is really a word, even though most spell-checkers don't recognize it as such. (Good for them!) It just doesn't mean what most people think it means. "Supposably" is discussed at length here, and in case you don't feel like clicking on the link, here's the section of the article which most succinctly describes the use and misuse of "supposably:"
Though the strict grammarians at BuzzFeed have lamented that our world is ending because so many people use supposably, it is a valid word that is recorded in several dictionaries of English, including Dictionary.com. However, it has historically carried a slightly different meaning than supposedly; supposably means “conceivably.” Most people use it interchangeably with supposedly, which is technically incorrect (despite the fact that the meaning is typically understood).
So there. Does that make everything clear?
But... you're not really one of those who uses "supposably" instead of "supposedly," are you?
Thanks for your time.