Formal definition: The condition of something occuring in the same space/time.

See the problem?

Saying that something "is just a coincidence" does not technically give any insight as to the lack of correlation.

When things coincide, they occur in the same point of space/time, whether they are related to each other is not explicit to this word.

But it is.

You have just experienced the phenomenon... of language evolution.

Join us next week... on the Twilight Zone.

Co*in"ci*dence (?), n. [Cf. F. coincidence.]

1.

The condition of occupying the same place in space; as, the coincidence of circles, surfaces, etc.

Bentley.

2.

The condition or fact of happening at the same time; as, the coincidence of the deaths of John Adams and Thomas Jefferson.

3.

Exact correspondence in nature, character, result, circumstances, etc.; concurrence; agreement.

The very concurrence and coincidence of ao many evidences . . . carries a great weight. Sir M. Hale.

Those who discourse . . . of the nature of truth . . . affirm a perfect coincidence between truth and goodness. South.

© Webster 1913.