Etymology
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streamline (n.)
1868, "line drawn from point to point, so that its direction is everywhere that of the motion of the fluid" [Lamb, "Hydrodynamics," 1906], from stream (n.) + line (n.). The adjective is attested from 1898, "free from turbulence," 1907 in sense of "shaped so that the flow around it is smooth."
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landline (n.)
also land-line, by 1861, originally a telegraph wire run over land (as opposed to under sea); from land (n.) + line (n.). Later (by 1965), a telephone line which uses wire or some other material (distinguished from a radio or cellular line).
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byline (n.)
also by-line, 1926, "line giving the name of the writer of an article in a newspaper or magazine;" it typically reads BY ________. From by (prep.) + line (n.). As a verb by 1942. Related: Bylined.
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curvilinear (adj.)

"having or consisting of curved lines," 1710, from curvi-, combining form of Latin curvus "curved, crooked, bent" (see curve (v.)) + linearis, from linea "line" (see line (n.)). Earlier was curvilineal (1650s).

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liner (n.1)
"vessel belonging to a shipping line," 1838, from line (n.) on notion of a succession of ships plying between ports along regular "lines," as distinguished from transient ships using those ports. (Line in this sense is attested by 1786 in reference to stagecoaches.) Earlier it meant "man of war, ship of the line" (1829). Meaning "cosmetic for highlighting the eyes" is from 1926. The type of baseball hit (forcible and parallel to the ground) was so called from 1874 (line drive is attested from 1899).
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interline (v.)
c. 1400, "make corrections or insertions between the lines of (a document)," from inter- "between" + line; perhaps modeled on Old French entreligniere or Medieval Latin interlineare "write between lines." Related: Interlined; interlining; interlineation.
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Mason-Dixon Line 

by 1779, named for Charles Mason and Jeremiah Dixon, English astronomers who surveyed (1763-7) the disputed boundary between the colonial holdings of the Penns (Pennsylvania) and the Calverts (Maryland). It became the technical boundary between "free" and "slave" states after 1804, when the last slaveholding state above it (New Jersey) passed its abolition act. As the line between "the North" and "the South" in U.S. culture, it is attested by 1834.

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rectilinear (adj.)

1650s, "forming a straight line," with -ar + rectiline (1560s), from Late Latin rectilineus, from rectus "straight" (from PIE root *reg- "move in a straight line," with derivatives meaning "to direct in a straight line") + linea "line" (see line (n.)). Of a figure, "bounded by straight lines," 1728. Related: Rectilineal "straight-lined" (1640s); rectilinearity.

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airline (n.)
also air-line, 1813, "beeline, straight line between two points on the earth's surface" (as through the air, rather than over terrain), from air (n.1) + line (n.). From 1853 and in later 19c. especially in reference to railways that ran directly between big cities in the U.S. instead of meandering from town to town in search of stock subscriptions as early railways typically did. Meaning "public aircraft transportation company" is from 1914.
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lines (n.)
1560s, "any short piece of writing" (especially poetry), from line (n.) in the sense "row of verse," attested since late Old English (answering to Latin versus, Greek stikhos). Hence "a few words in writing, a short letter" (1640s); meaning "words of an actor's part" is from 1882. From 1670s as "outlines, plans" (of a building, ship, etc.); hence, figuratively, "plan, model" of anything (1757). Lines of communication originally were transverse trenches in siegeworks, from line (n.) in a military sense "trench, rampart," a collective singular from 1690s given a new currency in World War I.
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