Q: I would like to know how it is possible to be charged with felony assault from a compulsive liars "word" no Witness

A: Unfortunately, this happens a lot. Especially if the accuser is in an intimate relationship with the accused person and the allegations involve domestic violence. A case like this, with a significant lack of evidence, is very defensible. Consult with an attorney ASAP to assess your best options.

A: I would be curious to know (and you may not know) if the felony classification is based on the alleged use of a deadly weapon, or an allegation that the "victim" suffered serious bodily injury or an allegation of strangulation. If the "victim" claimed any or all of those, the felony classification, without regard to the truth of the allegations, makes sense. In the absence of an allegation such as I have listed (there are others, but they do not seem relevant to your answer) then the assault, if there even was an assault, should be classified as a misdemeanor.

To get to your question more directly (how someone can be charged solely on the word of the alleged "victim".) The statement of a victim or witness is evidence. Evidence is the basis for the filing of any charge. There is no rule that says a crime cannot be charged on the word of a one person. The real question is how much weight should be given to that statement. Unfortunately, that question often goes unanswered until much later in the prosecution process, or until a jury answers the question. As Attorney Maye notes, the case you describe is very defensible (based on the facts you provide), and that can be said with even greater emphasis if the statement is uncorroborated by any other evidence.