active word-forming element in English and in many verbs inherited from French and Latin, from Latin de "down, down from, from, off; concerning" (see de), also used as a prefix in Latin, usually meaning "down, off, away, from among, down from," but also "down to the bottom, totally" hence "completely" (intensive or completive), which is its sense in many English words.

As a Latin prefix it also had the function of undoing or reversing a verb's action, and hence it came to be used as a pure privative — "not, do the opposite of, undo" — which is its primary function as a living prefix in English, as in defrost (1895), defuse (1943), de-escalate (1964), etc. In some cases, a reduced form of dis-.

late 14c., scannen, "to mark off verse in metric feet, analyze verse according to its meter," from Late Latin scandere "to scan verse," originally, in classical Latin, "to climb, rise, mount" (the connecting notion is of the rising and falling rhythm of poetry), from PIE *skand- "to spring, leap, climb" (source also of Sanskrit skandati "hastens, leaps, jumps;" Greek skandalon "stumbling block;" Middle Irish sescaind "he sprang, jumped," sceinm "a bound, jump").

English lost the classical -d- probably by confusion with suffix -ed (compare lawn (n.1)). Intransitive meaning "follow or agree with the rules of meter" is by 1857. The sense of "look at point by point, examine minutely (as one does when counting metrical feet in poetry)" is recorded by 1540s. New technology brought the meaning "systematically pass over with a scanner," especially to convert into a sequence of signals (1928). The (opposite) sense of "look over quickly, skim" is attested by 1926. Related: Scanned; scanning.

mid-15c. (adj.) "extending downward;" c. 1600 (n.) "an individual proceeding from an ancestor in any degree," from French descendant (13c.), present participle of descendre "to come down" (see descend).

Despite a tendency to use descendent for the adjective and descendant for the noun, descendant seems to be prevailing in all uses and appears 5 times more often than its rival in books printed since 1900. Compare dependant. In astrology, "the western horizon or cusp of the seventh house," 1680s.

1660s, "one who or that which descends," agent noun from descend. Specifically in typography, "part of a letter that extends below the body," 1802. Earlier in this sense was descendant (1670s).

"act of going down or downward," late 14c., from Old French descension and directly from Latin descensionem (nominative descensio) "a going down, descending," noun of action from past-participle stem of descendere "to come down" (see descend). Related: Descensional.

c. 1300, "genealogical extraction from an original or progenitor," from Old French descente "descent, descendance, lineage," formed from descendre "to come down" (see descend) on analogy of French nouns such as attente from attendre "to expect," vente "sale" from vendre "to sell," pente "slope" from pendre "to hang" (the etymological English word from Latin would be *descence).

Meanings "action of descending" (on); "act of passing from a higher to a lower place" in any way are from late 14c.; that of "a downward slope" is from 1590s. From c. 1600 as "a sudden invasion or attack." Biological sense "evolution" is from 1859 in Darwin, though there are uses which suggest essentially the same thing going back to 1630s.