When you study Latin so didn't look at the words and wrote "O Pineapple"...
Intellego :P The Ancient Greek o word for the vocative would be ω with omega and not omicron (ω ανανά if there was such a word in Ancient Greek)
Modern Greek doesn't use ο or ω in Vocative. It just uses the noun in the Vocative cause ;)
Why thank you for the information!
My Latin teacher was a speaker of Greek, and I think he is probably quite distressed with my terribleness right now!