word-forming element variously used with reference to images or to ideas, from Greek idea "form; the look of a thing; a kind, sort, nature; mode, fashion," in logic, "a class, kind, sort, species" (see idea).
before vowels phyl-, modern word-forming element, mostly in the sciences, often meaning "phylum," from Greek phylon, phylē "a tribe," also a political subdivision in ancient Athens, from base of phyein "to bring forth, produce, make to grow," whence also physis "nature" (from PIE root *bheue- "to be, exist, grow").
word-forming element in scientific compounds meaning "cartilage," from Latinized form of Greek khondros "cartilage" (of the breastbone), also "grain, grain of salt, seed, barley-grain," of uncertain origin. This is sometimes said to be from the PIE root meaning "to grind" which is the source of English grind (v.), but there are serious phonological objections and the word might be non-Indo-European [Beekes, "Etymological Dictionary of Greek"]. The body material so called for its gristly nature.
word-forming element of Greek origin meaning 1. "after, behind; among, between," 2. "changed, altered," 3. "higher, beyond;" from Greek meta (prep.) "in the midst of; in common with; by means of; between; in pursuit or quest of; after, next after, behind," in compounds most often meaning "change" of place, condition, etc. This is from PIE *me- "in the middle" (source also of German mit, Gothic miþ, Old English mið "with, together with, among").
The notion of "changing places with" probably led to the senses of "change of place, order, or nature," which was a principal meaning of the Greek word when used as a prefix (but it also denoted "community, participation; in common with; pursuing").
The third, modern, sense, "higher than, transcending, overarching, dealing with the most fundamental matters of," is due to misinterpretation of metaphysics (q.v.) as "science of that which transcends the physical." This has led to a prodigious erroneous extension in modern usage, with meta- affixed to the names of other sciences and disciplines, especially in the academic jargon of literary criticism: Metalanguage (1936) "a language which supplies terms for the analysis of an 'object' language;" metalinguistics (by 1949); metahistory (1957), metacommunication, etc.