ceiling (n.)

late 14c., "pertaining to the sky or the visible heavens; pertaining to the Christian or pagan heaven," from Old French celestial "celestial, heavenly, sky-blue," from Latin caelestis "heavenly, pertaining to the sky," from caelum "heaven, sky; abode of the gods; climate," which is of uncertain origin; perhaps from PIE *kaid-slo-, perhaps from a root also found in Germanic and Baltic meaning "bright, clear" (compare Lithuanian skaidrus "shining, clear;" Old English hador, German heiter "clear, shining, cloudless," Old Norse heið "clear sky").

The Latin word is the source of the usual word for "sky" in most of the Romance languages, such as French ciel, Spanish cielo, Italian cielo, Portuguese céu. Transferred sense of "heavenly, very delightful" in English is from early 15c. Celestial Empire "China" is from 1808, translating native names.

third letter of the Latin alphabet. Alphabetic writing came to Rome via the southern Etruscan "Caeretan" script, in which gamma was written as a crescent. Early Romans made little use of Greek kappa and used gamma for both the "g" and "k" sounds, the latter more frequently, so that the "k" sound came to be seen as the proper one for gamma. Classical Latin -c-, with only the value "k," passed to Celtic and, via missionary Irish monks, to the Anglo-Saxons. Also see cee.

In some Old English words, before some vowels and in certain positions, -c- had a "ts" sound that was respelled ch- in Middle English by French scribes (chest, cheese, church; see ch). In Old English -k- was known but little used.

Meanwhile, in Old French, many "k" sounds drifted to "ts" and by 13c., "s," but still were written -c-. Thus the 1066 invasion brought to the English language a flood of French and Latin words in which -c- represented "s" (as in cease, ceiling, circle) and a more vigorous use of -k- to distinguish that sound. By 15c. even native English words with -s- were being respelled with -c- for "s" (ice, mice, lice).

In some English words from Italian, the -c- has a "ch" sound (via a sound evolution somewhat like the Old French one). In German, -c- in loanwords was regularized to -k- or -z- (depending on pronunciation) in the international spelling reform of 1901, which was based on the Duden guide of 1880.

As a symbol in the Roman numeral system, "one hundred;" the symbol originally was a Greek theta, but was later reduced in form and understood to stand for centum. In music, it is the name of the keynote of the natural scale, though the exact pitch varied in time and place 18c. and 19c. from 240 vibrations per second to 275; it wasn't entirely regularized (at 261.63) until the adoption of the A440 standard in the 1930s. C-spring as a type of carriage spring is from 1794, so called for its shape.