Wonderland

Thank-you both so much, a lot less confused now!

The definition my science booklet has for a base is a substance with an OH- ion. I told my teacher that I thought the definition in the book might have had limitations and he basically made me feel like a complete idiot. However, I thought ammonia was basic but NH3 doesn't have OH. I probably am wrong here, but could someone please explain to me why I'm wrong because I'm really confused. Is it only a base in solution or something? Because I thought it could react in gaseous form and operate as a base. As I'm fairly certain it's quite obvious, I don't really know a whole lot, so a little help and an explanation as to what I have done wrong would be really helpful. Thank you