You don't hear words that start with Z much. It must be a very small section of the dictionary.
Towards the end of the definition section of the dictionary, you will find words that start with ZO, like zoo and zoology. I know they come from a Greek word, zoi, which means life.
Zeal and zest are not much different.
Zeal means enthusiasm, passion, fervor. From Latin, originally from Greek.
Zest means enjoyment, relish. (And also lemon or orange flavoring from the peels.) From French. The closest synonyms are savory, and Piquant. (That could be the subject of a future article for the philologue. Pi-quant! Well, it sure doesn't come from Greek!)
Zesty means hot (temperature-wise) in Greek.
Zealous and Zestful are adjectives, while Zeal and Zest are nouns. A person with Zeal is a zealot. A person with Zest is a ... carefree living treasure?
If you live to be 97 in Okinawa (and lots do!), you have a special birthday celebration, called a ka-jee-maya, and they call you a Living National Treasure. I will discuss this in my next class, The Hypnotic Fountain of Youth, starting Sept 17, at 7 pm, at the Unity Church of Palm Harbor. See
http://verbalimpact.blogspot.com/ for details.