知っているのが「機会」と「チャンス」だけです。

Both can be used as in "don't miss this opportunity", but chansu obviously came from english and kikai perhaps from chinese.

I looked up in my jisho,too. I usulally do not use 契機.

契機and 時機are almost the same and rarely used.

機会is the best equivalent for "opportunity".

ありがとうございます！

Thanks a lot for your answers !