coincidence · noun C or U /koʊˈɪn.səd.əns/Full view
B2 when two very similar things happen at the same time but there is no reason for it
Dictionary examples:

You chose exactly the same wallpaper as us - what a coincidence!

Just by coincidence I met my old friend and classmate again fifty years later.

It was pure coincidence that we met.

Learner example:

What a coincidence, don't you think so? (First Certificate in English; B2; Portuguese)

Cambridge logo