I've tried saying the word "psee", but it is very hard. The best I can do is "p-see"
It's the same sound that occurs in English words such lips, lipstick, lapse, collapse, lopsided and upside, if that helps (that's all I can think right now).
Would 'ψή' be accepted? I thought that second character made an 'ee' sound?
I think thats more like an ē sound.
ήτα - eta - [ē] This is what I get when searching for it.