thesaurus says:

Main Entry: zest
Part of Speech: noun
Definition: energy
Synonyms: appetite, ardor, bliss, bounce, cheer, delectation, delight, eagerness, ecstasy, elation, enjoyment, enthusiasm, fervor, gusto, guts, happiness, keenness, moxie, passion, pep, pleasure, relish, satisfaction, zeal, zing
Antonyms: apathy, indifference, lethargy

www.thesaurus.com