Bi- vs. Buy vs. By vs. Bye

Two or twice

He has his teeth cleaned bi-yearly; every six months.

obtain by purchase; acquire by means of a financial transaction

She buys for the big department store

Used in specifying adjacent dimensions or next to, or an agent of a passive action

a room ten by twenty meters, He stood by the door. Or The book was written by Jack Straw.

An informal farewell remark

Bye, I'll see you later.