1.NounAn issue concerning the factual circumstances of a cause of action that is to be tried or proved; an allegation forming the basis of a claim or defense, as opposed to a matter of law.
"Whether he left his house on the night of the murder is a matter of fact."
2.NounA point of fact; a claim or statement about (empirical) facts, as opposed to conjecture or opinion.
"It’s a matter of fact that I came into work yesterday."