"science of animals," 1660s, from Modern Latin zoologia, from Greek zoion "animal" (from PIE root *gwei- "to live") + -logia "study" (see -logy).
-ical
compound adjectival word-forming element, usually interchangeable with -ic but sometimes with specialized sense (such as historic/historical, politic/political), Middle English, from Late Latin -icalis, from Latin -icus + -alis (see -al (1)). Probably it was needed because the forms in -ic often took on a noun sense (for example physic). Forms in -ical tend to be attested earlier in English than their twins in -ic.
zoo n.
c. 1847, short for Zoological Gardens of the London Zoological Society, established 1828 in Regent's Park to house the society's collection of wild animals. The first three letters taken as one syllable. "From a mere vulgarism, this corruption has passed into wide colloquial use" [Century Dictionary]. Slang meaning "crowded and chaotic place" first recorded 1935.