2. A short account of an incident; especially, a biographical one.
3. An interesting incident or brief history; story, tale, short narrative; sometimes, a humorous account: "Have you noticed that many public speakers begin their talks with humorous anecdotes?"
4. A particular or detached incident or fact of an interesting nature; a biographical incident or fragment; a single passage of private life.
Even among the ancient Greeks, there were two kinds of stories: those given out publicly and those only known privately.
The latter kind was called anekdotos "not published". The word was formed by combining a, an, "not", and ekdotos, "given out". From this source comes French anecdote and then English anecdote which originally kept the Greek significance of "unpublished narratives".
An "unpublished narrative", especially about interesting things and famous people, has a ready market; so anecdotes are eagerly brought out on every occasion, and the word lost its original sense, coming to mean simply "a story, an incident".