bye

Từ điển American Heritage Dictionary 4th

I. bye¹ also by (bī)n.
1. A secondary matter; a side issue.
2. Sports. The position of one who draws no opponent for a round in a tournament and so advances to the next round.Idiom:by the bye/by
By the way; incidentally. [From by¹.] II. bye² (bī)interj.
Used to express farewell. [Short for goodbye.]