Greek 'zoion' (animal) + 'logos' (study) — same root gave us 'zoo' and 'zodiac' (the little animals).
The scientific study of the behavior, structure, physiology, classification, and distribution of animals.
From modern Latin 'zoologia' (17th century), a scholarly compound of Greek 'zōion' (ζῷον, animal, living being) and '-logia' (λογία, the study of, discourse about), from 'logos' (λόγος, word, reason, account). Greek 'zōion' is the neuter of 'zōios' (living), from 'zōē' (ζωή, life), from PIE *gʷyeh₃- (to live) — the same root that gives Latin 'vīta' and English 'vital.' The suffix '-logy' traces to PIE *leg