What is the X in X-mas?
1580s, "natural science," from physic in sense of "natural science." Also see -ics. Based on Latin physica (neuter plural), from Greek ta physika, literally "the natural things," name of Aristotle's treatise on nature. Specific sense of "science treating of properties of matter and energy" is from 1715.
c.1300, fysike, "art of healing, medical science," also "natural science" (c.1300), from Old French fisike "natural science, art of healing" (12c.) and directly from Latin physica (fem. singular of physicus) "study of nature," from Greek physike (episteme) "(knowledge) of nature," from fem. of physikos "pertaining to nature," from physis "nature," from phyein "to bring forth, produce, make to grow" (cf. phyton "growth, plant," phyle "tribe, race," phyma "a growth, tumor") from PIE root *bheue- "to be exist, grow" (see be). Spelling with ph- attested from late 14c. (see ph). As a noun, "medicine that acts as a laxative," 1610s. The verb meaning "to dose with medicine" is attested from late 14c.
physics phys·ics (fĭz'ĭks)
Abbr. phys. The science of matter and energy and of interactions between the two, grouped in traditional fields such as acoustics, optics, mechanics, thermodynamics, and electromagnetism, as well as in modern extensions including atomic and nuclear physics, cryogenics, solid-state physics, particle physics, and plasma physics.
Physical properties, interactions, processes, or laws.
physic phys·ic (fĭz'ĭk)
A medicine or drug, especially a cathartic.