Etymology
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ladder (n.)
Old English hlæder "ladder, steps," from Proto-Germanic *hlaidri (source also of Old Frisian hledere, Middle Dutch ledere, Old High German leitara, German Leiter), from suffixed form of PIE root *klei- "to lean" (source also of Greek klimax "ladder"). In late Old English, rungs were læddrestæfæ and the side pieces were ledder steles. The belief that bad things happen to people who walk under ladders is attested from 1787, but its origin likely is more scientific than superstitious.
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step-ladder (n.)
also stepladder, one with flat steps instead of rungs, 1728, from step (n.) + ladder.
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ladder-back (adj.)
1898 as a type of chair, from ladder (n.) + back (n.).
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Baqubah 
city in Iraq, from Arabic baya 'kuba "Jacob's house."
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Milky Way (n.)

"the galaxy as seen in the night sky," late 14c., loan-translation of Latin via lactea; see galaxy. Formerly in Middle English also Milken-Way and Milky Cercle. The ancients speculated on what it was; some guessed it was a vast assemblage of stars (Democrates, Pythagoras, even Ovid); the question was settled when Galileo, using his telescope, reported that the whole of it was resolvable into stars. Old native names for it include Jacob's Ladder, the Way to St. James's, and Watling Street (late 14c.).

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Jacob 

masc. proper name; Old Testament patriarch, son of Isaac and Rebecca and father of the founders of the twelve tribes, from Late Latin Iacobus, from Greek Iakobos, from Hebrew Ya'aqobh, literally "one that takes by the heel; a supplanter" (Genesis xxv.26), a derivative of 'aqebh "heel." The most popular name for boys born in the U.S. from 1999 through 2008. Jacob's ladder, in various transferred uses from 1733, is from Genesis xxviii.12. In Spanish as Jago, Iago, also Diego; with alterations as Italian Giacomo, James, and (contracted) Spanish Jaime.

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echelon (n.)
1796, echellon, "step-like arrangement of troops," from French échelon "level, echelon," literally "rung of a ladder," from Old French eschelon, from eschiele "ladder," from Late Latin scala "stair, slope," from Latin scalae (plural) "ladder, steps," from PIE *skand- "to spring, leap" (see scan (v.)). Sense of "level, subdivision" is from World War I.
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pompier (n.)

"fireman's scaling ladder," short for pompier ladder (by 1893), French, literally "fireman," from pompe "pump" (see pump (n.1)).

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scalar (adj.)

1650s, "resembling a ladder," from Latin scalaris "of or pertaining to a ladder," from scalae (plural) "ladder, steps, flight of steps" (see scale (n.2)). The noun in the mathematical sense of "a real number" is from 1846, coined by Irish mathematician William R. Hamilton (1805-1865), who can explain why it is the correct word for that.

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Dinah 
fem. proper name, in the Old Testament, Jacob's daughter by Leah, from Hebrew Dinah, literally "judgment," from din "to judge."
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