Is there any difference between 'coincident' and 'coincidental' ?
Both of them are adjective, when should we use them ?

thanks .

Question

Is there any difference between 'coincident'  and 'coincidental' ?
Both of them are adjective, when should we use them ? 

thanks .

Answer

coincidental is more common than coincident. A LOT more common. Don't worry about using coincident in everyday conversation.

Btw, the noun form (coincidence) is most common. "What a coincidence!" means 真巧.

Answer

It is a coincidence that we are here at the same time.  It was a coincidental meeting.  This means it was by chance.  Nothing causes a coincidence.  It just happens. You would not need to use the word coincident.
coincidence is a noun.  coincidental _______ is an adjective.