E plural-bus unum

Then I started pondering why we spell it "hippos" instead of "hippoes". And, is the plural of "hippopotamus" "hippopotami" because it's Latin, or should it be something else because it was a Greek word before the ancient Romans used it? (I once took a Latin course, but as far as other dead languages, they're all Greek to me.)

I have Betty Crocker's Cooky Book at home. I guess that's the proper singular form of "cookies", but it looks funny. Then again, I always eat cookies; I never eat a single cooky.

One plural which often is misspelled is the plural of "bus". The correct spelling is "buses". Whenever I see "busses", I wonder what kisses have to do with what I'm reading.