Merriam-Webster Online Dictionary
Here is a better definition from Merriam-Webster Dictionary.
Main Entry: her·e·tic
Pronunciation: 'her-&-"tik
Function: noun
1 : a dissenter from established church dogma; especially : a baptized member of the Roman Catholic Church who disavows a revealed truth
2 : one who dissents from an accepted belief or doctrine : NONCONFORMIST
...we saw one casting out devils in thy name, and he followeth not us: and we forbade him, because he followeth not us.
But Jesus said, Forbid him not: for there is no man which shall do a miracle in my name, that can lightly speak evil of me. For he that is not against us is on our part."
He gave you the formal definition of heresy as held by both Orthodox and Catholics. You respond with Webster's definition. Do you know anything about language? Websters and all other general dictionaries merely seek to report the common usage for a word. As usage changes, new editions reflect it. The definition you give reflects common usage of the word heretic.
The definition Bohemund posted is the definition the Church has always used. Even Presbyterians and Episcopalians use it when they put someone on trial for heresy, e.g, Charles Finney in the 1800s and more recently, some Episcopalian wackos.
The key element in defining heresy theologically is that it must be a really chosen error in biblical interpretation (in theology). The Greek word simply means choice. To make a real choice one must first have knowledge of the various choices. So no one can be an unwitting heretic. The second major element is that one must persist in this knowing choice. That's why heretics (those making erroneous doctrinal choices knowingly) are first formally put on notice that their beliefs are erroneous. Only if they do not change their position are they heretics because at that point they are pertinacious.
You meet the second criterion (pertinacity) but not the first. Not because you have not been put on notice but because you seem to be incapable of understanding relatively simple reasoning.