This word is one of the banes of my existence: Supposably. It's commonly used in lieu of Supposedly. It is a real word, but with quite an obscure definition: it means that something is CAPABLE OF being supposed, not what IS being supposed - which is how it's typically used. Here is more:
Supposed(ly): Something that is or has been supposed, a supposed fact, or true without personal knowledge.
Supposedly, he has a post-graduate education; he is an attorney, after all.
In other words, what is being supposed it the level of the attorney's education. The speaker may not have the attorney's transcripts to prove or disprove the attorney's education, but common knowledge indicates that higher education is required for attorneys, as well as bar exams, supposedly.
Supposable(y): Something that could be supposed.
Example: Supposably, my dog could fly to the moon.
In other words, it could be supposed that my dog can fly to the moon, but of course, that would be ridiculous.
As ridiculous as the use of supposABLY when speakers REALLY mean to say supposEDLY.