0 said when you are surprised, pleased, disappointed, etc. -- vaya
1 used to introduce an idea that you have just thought of, or something that you have just remembered -- ¡ah!
2 written abbreviation for the US state of Ohio: used in addresses -- abreviatura escrita de “Ohio”
3 indicates surprise, disappointment, sympathy, etc. -- oh
4 used at the beginning of a sentence, especially a reply -- oh