1. rule; regulation
そうしなければいけない決まりなど、ないでしょう。There is no rule that says you must do so, is there?
2. settlement; conclusion; end; agreement; arrangement
これで決まりだろう。This settles it.
3. habit; custom; habitual way
4. countenance in front of another person; face
usu. as 決まりが悪い, etc.
5. love relationship between a customer and a prostitute