A coincidence is the surprising occurrence of two things at the same time, by pure chance. "A small boy hit a lamppost with a stick. By pure coincidence, that was the exact instant when the there was a power blackout. Every light in the city went out. The terrified child thought he had done it." "Irony" has several meanings. One of them is making a bitter joke by saying the opposite of what one means. For example, someone in a fast sports car, hopelessly stuck in a traffic jam, might say, ironically, "Thank goodness I'm driving a Ferrari." "Irony" is often used to mean a tragic coincidence. For example, if a member of the band named Anthrax were to die of anthrax, some people would call that an "ironic death." Some people think this is not a correct use of the word "irony," but it is very common.

Coincidence http://dictionary.cambridge.org/dictionary/british/coincidence?q=Coincidence Irony http://dictionary.cambridge.org/dictionary/british/irony?q=Irony