word-forming element meaning "wax, waxy," from Latinized form of Greek kēros "beeswax," a word of unknown origin with no obvious ulterior connections. "As there is no evidence for Indo-European apiculture, we have to reckon with foreign origin for κηρός" [Beekes].
before vowels actin-, word-forming element meaning "pertaining to rays," from Latinized form of Greek aktis (genitive aktinos) "ray of light, beam of light; spoke of a wheel;" a word of unknown etymology. It is perhaps cognate with Sanskrit aktuh "light, ray," Gothic uhtwo "dawn, daybreak," Lithuanian anksti "early" [Beekes].
word-forming element meaning "light" or "photographic" or "photoelectric," from Greek photo-, combining form of phōs (genitive phōtos) "light" (from PIE root *bha- (1) "to shine").
before vowels phaner-, word-forming element meaning "visible, manifest," especially from 18c. in biology, from Greek phaneros "visible, manifest, evident, apparent," from phainein "bring to light, cause to appear, show," from PIE root *bha- (1) "to shine." Opposed to crypto-.
before vowels xanth-, word-forming element meaning "yellow," from Greek xanthos "yellow" of various shades; used especially of hair and horses, of unknown origin. Used in scientific words; such as xanthein (1857) "soluble yellow coloring matter in flowers," xanthophyll (1838) "yellow coloring matter in autumn leaves." Also Huxley's Xanthochroi (1867) "blond, light-skinned races of Europe" (with ōkhros "pale").
before vowels pneum-, word-forming element meaning "lung," from Greek pneumōn "lung," altered (probably by influence of pnein "to breathe") from pleumōn (which was an alternative form in Attic), literally "floater," probably cognate with Latin pulmo "lung(s)," from PIE root *pleu- "to flow." The notion perhaps is from the fact that, when thrown into a pot of water, lungs of a slaughtered animal float, while the heart, liver, etc., do not (compare Middle English lights "the lungs," literally "the light (in weight) organs"). Greek pneumōn also meant "jellyfish, medusa," "perhaps from its rhythmical pulsation, as if breathing" [Thompson].