double-decker (n.)

c. 1300, "twice as much or as large," also "repeated, occurring twice," also "of extra weight, thickness, size, or strength; of two layers," from Old French doble (10c.) "double, two-fold; two-faced, deceitful," from Latin duplus "twofold, twice as much," from duo "two" (from PIE root *dwo- "two") + -plus "more" (see -plus).

From early 14c. as "having a twofold character or relation," also "consisting of two in a set together; being a pair, coupled." From mid-14c. as "characterized by duplicity." The earliest recorded use in English is c. 1200, in double-feast "important Church festival."

Double-chinned is from late 14c.; double-jointed, of persons, is by 1828. Military double time (1833) originally was 130 steps per minute; double quick (adj.) "very quick, hurried" (1822) originally was military, "performed at double time."

The photographic double exposure is by 1872. The cinematic double feature is by 1916. Double figures "numbers that must be represented numerically by two figures" is by 1833. Double-vision is by 1714. Double indemnity in insurance is by 1832; double jeopardy is by 1817. The baseball double play is by 1866.

Double trouble "twice the trouble" is by 1520s; in 19c. America it was the name of a characteristic step of a rustic dance or breakdown, derived from slave dancing on plantations. A double-dip (n.) originally was an ice-cream cone made with two scoops (1936); the figurative sense is by 1940. Double bed "bed made to sleep two persons" is by 1779. Double life "a sustaining of two different characters in life" (typically one virtuous or respectable, the other not) is by 1888.

mid-15c., dekke, "covering extending from side to side over part of a ship," from a nautical use of Middle Dutch dec, decke "roof, covering," from Proto-Germanic *thakam (source also of thatch (n.)), from PIE root *(s)teg- "to cover."

Sense extended early in English from "covering" to "platform of a ship." Meaning "pack of cards necessary to play a game" is from 1590s, perhaps because they were stacked like decks of a ship. Tape-deck (1949) is in reference to the flat surface of old reel-to-reel tape recorders. 

Deck-chair (1844) so called because they were used on ocean liners. On deck (by 1740) was in nautical use especially "ready for action or duty;" extended sense in baseball, of a batter waiting a turn at the plate, is by 1867. To clear the deck (1852) is to prepare a ship for action; it is perhaps a translation of French débarasser le pont.