word-forming element meaning "many, much, multi-, one or more," from Greek polys "much" (plural polloi), from PIE root *pele- (1) "to fill," with derivatives referring to multitudinousness or abundance. Equivalent to Latin multi-, it is properly used in compounds only with words of Greek origin. In chemical names, usually indicating a compound with a large number of atoms or molecules of the same kind (such as polymer).
1620s, "bedridden person, one confined to his bed by sickness," from French clinique (17c.), from Latin clinicus "physician that visits patients in their beds," from Greek klinike (techne) "(practice) at the sickbed," from klinikos "of the bed," from kline "bed, couch, that on which one lies," from suffixed form of PIE root *klei- "to lean."
Also "one who defers baptism until the death-bed" (1660s). Sense of "private hospital" is from 1884, from German Klinik in this sense, itself from French clinique, via the notion of "bedside medical education, examination of a patient by an instructor in the presence of students." The modern sense thus reverses the classical one, in which the "clinic" came to the patient. General sense of "conference for group instruction in something" is from 1919.