Etymology
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quadrangle (n.)

late 14c., "a plane figure having four angles; a rectangle, square, etc.," from Old French quadrangle (13c.) and directly from Late Latin quadrangulum "four-sided figure," noun use of neuter of Latin adjective quadrangulus "having four corners," from Latin quattuor "four" (from PIE root *kwetwer- "four") + angulus "angle" (see angle (n.)). Meaning "four-sided court nearly surrounded by buildings" is from 1590s.

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rectangle (n.)

in geometry, "quadrilateral plane figure having all its angles right and all its opposite sides equal," 1570s, from French rectangle (16c.), from rect-, combining form of Latin rectus "right" (from PIE root *reg- "move in a straight line," with derivatives meaning "to direct in a straight line") + Old French angle (see angle (n.)). Late/Medieval Latin rectiangulum meant "a triangle having a right angle," noun use of neuter of rectiangulus "having a right angle." When the adjacent sides are equal, it is a square, but rectangle usually is limited to figures where adjacent sides are unequal.

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anchor (n.)
"device for securing ships to the ground under the water by means of cables," Old English ancor, borrowed 9c. from Latin ancora "an anchor," from or cognate with Greek ankyra "an anchor, a hook," from PIE root *ang-/*ank- "to bend" (see angle (n.)).

A very early borrowing into English and said to be the only Latin nautical term used in the Germanic languages (German Anker, Swedish ankar, etc.). The unetymological -ch- emerged late 16c., a pedantic imitation of a corrupt spelling of the Latin word. The figurative sense of "that which gives stability or security" is from late 14c. Meaning "host or presenter of a TV or radio program" is from 1965, short for anchorman (q.v.).
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ankle (n.)

14c. ancle, ankle, from Old English ancleow "ankle," ultimately from PIE root *ang-/*ank- "to bend" (see angle (n.)). The Middle English and modern form of the word seems to be from or influenced by Old Norse ökkla or Old Frisian ankel, which are immediately from the Proto-Germanic form of the root, *ankjōn-(source also of Middle High German anke "joint," German Enke "ankle").

The second element in the Old English, Old Norse and Old Frisian forms perhaps is a folk-etymology suggestion of claw (compare Dutch anklaauw), or it may be from influence of cneow "knee," or it may be the diminutive suffix -el. Middle English writers distinguished inner ankle projection (hel of the ancle) from the outer (utter or utward ancle), and the word sometimes was applied to the wrist (ankle of þe hand).

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Anglo-Saxon (n.)

Old English Angli Saxones (plural), from Latin Anglo-Saxones, in which Anglo- is an adjective, thus literally "English Saxons," as opposed to those of the Continent (now called Old Saxons). Properly in reference to the Saxons of ancient Wessex, Essex, Middlesex, and Sussex.

I am a suthern man, I can not geste 'rum, ram, ruf' by letter. [Chaucer, "Parson's Prologue and Tale"]

After the Norman-French invasion of 1066, the peoples of the island were distinguished as English and French, but after a few generations all were English, and Latin-speaking scribes, who knew and cared little about Germanic history, began to use Anglo-Saxones to refer to the pre-1066 inhabitants and their descendants. When interest in Old English writing revived late 16c., the word was extended to the language we now call Old English.

In the last years of the reign of Elizabeth, Camden revived the use of the old name Anglosaxones, and, probably for the first time, used lingua Anglosaxonica for the language of England before the Norman conquest. He explains that Anglosaxones means the Saxons of England, in contradistinction to those of the continent; and, in his English Remains, he, accordingly, renders it by "English Saxons." Throughout the seventeenth century, and even later, "English Saxon" continued to be the name ordinarily applied by philologists to the language of king Alfred, but, in the eighteenth century, this gave place to "Anglo-Saxon." [Henry Bradley, in "Cambridge History of English Literature," 1907]

It has been used rhetorically for "English" in an ethnological sense from 1832, and revisioned as Angle + Saxon.

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diagonal (adj.)

early 15c. (implied in diagonally), "extending as a line from one angle to another not adjacent," from Old French diagonal, from Latin diagonalis, from diagonus "slanting line," from Greek diagonios "from angle to angle," from dia "across, through" (see dia-) + gōnia "angle, corner" (from PIE root *genu- (1) "knee; angle").

As a noun, from 1570s, "straight line drawn from one angle to or through another not adjacent, in a plane or solid figure." In chess, "a line of squares running diagonally across a board."

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agonic (adj.)

"having no angle," 1846, from Greek agonos, from a- "not" (see a- (3)) + -gonos "angled," from gōnia "angle, corner" (from PIE root *genu- (1) "knee; angle"). In reference to the imaginary line on the earth's surface connecting points where the magnetic declination is zero.

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goniometer (n.)

instrument for measuring solid angles, 1766, from Greek gōnia "corner, angle" (from PIE root *genu- (1) "knee; angle") + -meter. Related: Goniometry.

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heptagon (n.)

1560s, from French heptagon, from Greek heptagonon, from hepta "seven" (see septi-) + gōnia "angle, corner" (from PIE root *genu- (1) "knee; angle"). Related: Heptagonal.

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trigonometry (n.)

"branch of mathematics that deals with relations between sides and angles of triangles," 1610s, from Modern Latin trigonometria (Barthelemi Pitiscus, 1595), from Greek trigonon "triangle" (from tri- "three" (see tri-) + gōnia "angle, corner" (from PIE root *genu- (1) "knee; angle") + metron "a measure" (from PIE root *me- (2) "to measure").

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