"connected with or relating to the duodenum," 1754; see duodenum + -al (1).

"relating to the number twelve, twelve-fold," 1766, from Latin duodenarius "containing twelve," from duodeni "twelve each," from duodecim "twelve" (see dozen).

"first portion of the small intestine," late 14c., also duodene, from Medieval Latin duodenum digitorium "space of twelve digits," from Latin duodeni "twelve each" (from duodecim "twelve;" see dozen). Coined by Gerard of Cremona (d. 1187) in "Canon Avicennae," a loan-translation of Greek dodekadaktylon, literally "twelve fingers long." The intestine part was so called by Greek physician Herophilus (c. 353-280 B.C.E.) for its length, which is about equal to the breadth of twelve fingers. The classical plural is duodena.

"one easily deceived or led astray by false representations," 1680s, from French dupe "deceived person," from duppe (early 15c.), thieves' jargon, perhaps from phrase de huppe "of the hoopoe," an extravagantly crested and reputedly stupid bird. For names of supposedly stupid birds applied to stupid persons, compare booby, goose (n.), gull (n.2).

"to deceive, trick, mislead by imposing on one's credulity," 1704, from dupe (n.). Related: Duped; duping.

1817, "composed of two parts, double, twofold," from Latin duplex "twofold," from duo "two" (from PIE root *dwo- "two") + -plex, from PIE root *plek- "to plait." The noun in the sense of "house or other building so divided that it forms two dwelling places" (also sometimes "two-story apartment") is American English, by 1922.

early 15c., "having two parts, double," from Latin duplicatus, past participle of duplicare "to double," from duo "two" (from PIE root *dwo- "two") + plicare "to fold" (from PIE root *plek- "to plait"). Meaning "exactly corresponding, that is an exact copy of" is from 1812.

late 15c., "to repeat, produce a second (like the first);" 1620s, "to double," from Latin duplicatus, past participle of duplicare "to double," from duo "two" (from PIE root *dwo- "two") + plicare "to fold" (from PIE root *plek- "to plait"). Related: Duplicated; duplicating.

1530s, "one of two or more things corresponding in every respect to each other," from duplicate (adj.). From 1701 as "another corresponding to a first or original, an exact counterpart or double of an original."

early 15c., "act of doubling," from Old French duplicacion (13c.) and directly from Latin duplicationem (nominative duplicatio), noun of action from past-participle stem of duplicare "to double" (see duplicate (adj.)). Sense of "act of making or repeating something essentially the same" is from 1580s. Meaning "a duplicate copy or version" is by 1872.