1640s, "substance or organism that shines of itself," from Latin phosphorus "light-bringing," also "the morning star" (a sense attested in English from 1620), from Greek Phosphoros "morning star," literally "torchbearer," from phōs "light," contraction of phaos "light, daylight" (related to phainein "to show, to bring to light," from PIE root *bha- (1) "to shine") + phoros "bearer," from pherein "to carry" (from PIE root *bher- (1) "to carry," also "to bear children").
As the name of a solid, non-metallic, combustible chemical element, it is recorded from 1680, originally one among several substances so called; the word used exclusively of the element from c. 1750. It was discovered in 1669 by Henning Brand, merchant and alchemist of Hamburg, who derived it from urine. Lavoisier demonstrated it was an element in 1777. According to Flood, "It is the first element whose discoverer is known."
word-forming element making adjectives from nouns, meaning "having, full of, having to do with, doing, inclined to," from Old French -ous, -eux, from Latin -osus (compare -ose (1)). In chemistry, "having a lower valence than forms expressed in -ic."