Any old irony

Certain words I find myself looking up in a dictionary 2 or 3 times a year going back years. The definition never quite persuades or sticks.
One of them is ‘irony’. Of course I can label the situation ‘ironic’ when a bus driver gets run over by a bus and know that I am on safe ground, even though he obviously was not. I recognise, but cant connect to the squashed bus driver, dramatic irony but wonder whether a film that lacked dramatic irony at its first outing acquires it when you see the repeat. I see Socratic irony turning up too. What I cant see is what connects these various things what are the necessary and sufficient conditions that hold together the concept of irony?.