Etymology
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cohort (n.)

early 15c., "company of soldiers, band of warriors," from French cohorte (14c.) and directly from Latin cohortem (nominative cohors) "enclosure," with meaning extended to "infantry company" in the Roman army through the notion of "enclosed group, retinue;" from assimilated form of com "with" (see co-) + a root akin to hortus "garden," from PIE *ghr-ti-, from PIE root *gher- (1) "to grasp, enclose."

Sense of "accomplice" is first recorded 1952, American English, from meaning "group united in common cause" (1719). In demographics, "group of persons having a common statistical characteristic" (originally being born in the same year), 1944.

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study (v.)

early 12c., "to strive toward, devote oneself to, cultivate" (translating Latin occupatur), from Old French estudiier "to study, apply oneself, show zeal for; examine" (13c., Modern French étudier), from Medieval Latin studiare, from Latin studium "study, application," originally "eagerness," from studere "to be diligent," from PIE *(s)teu- (1) "to push, stick, knock, beat" (see steep (adj.)). The notion appears to be "pressing forward, thrusting toward," hence "strive after."

Martha swanc and becarcade to geforðigene þan Hælende and his þeowen þa lichamlice behefðen. Seo studdede emb þa uterlice þing. [Homily for the Feast of the Virgin Mary, c.1125]

From c. 1300 as "apply oneself to the acquisition of learning, pursue a formal course of study," also "read a book or writings intently or meditatively." From mid-14c. as "reflect, muse, think, ponder." Meaning "regard attentively" is from 1660s. Related: Studied; studying.

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study (n.)

c. 1300, "application of the mind to the acquisition of knowledge, intensive reading and contemplation of a book, writings, etc.," from Old French estudie "care, attention, skill, thought; study, school" (Modern French étude), from Latin studium "study, application" (see study (v.)). Also from c. 1300 as "a state of deep thought or contemplation; a state of mental perplexity, doubt, anxiety; state of amazement or wonder." From mid-14c. as "careful examination, scrutiny." Sense of "room furnished with books" is from late 14c. Meaning "a subject of study" is from late 15c. Study hall is attested from 1891, originally a large common room in a college.

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cahoots (n.)

"company, partnership," 1829, Southern and Western American English, of unknown origin; said [OED] to be perhaps from French cahute "cabin, hut" (12c.), but U.S. sources [Bartlett] credit it to French cohorte (see cohort), which is said to have had a sense of "companions, confederates."

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oology (n.)

"the study of birds' eggs," 1823, from oo- "egg" + -logy "study of." Related: Oological; oologist.

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oncology (n.)

"the scientific study of tumors," 1857, coined in English from onco- "tumor" + -logy "science or study of." Related: Oncologist; oncological.

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pathology (n.)

"science of diseases," 1610s, from French pathologie (16c.), from medical Latin pathologia "study of disease," from Greek pathos "suffering" (from PIE root *kwent(h)- "to suffer") + -logia "study" (see -logy). In reference to the study of abnormal mental conditions from 1842. Ancient Greek pathologia was "study of the passions;" the Greek word for "science of diseases" was pathologike ("pathologics").

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rheology (n.)

"study of the deformation of the flow of matter," 1929, from French rhéologie; see rheo- "current of a stream" + -logy "study of." Related: Rheologist; rheological.

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unstudied (adj.)

late 14c., "not made a subject of study," from un- (1) "not" + past participle of study (v.). From 1650s as "natural, not artificial."

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lithology (n.)

"the study of rock-formation," a branch of geology, 1716, from Modern Latin lithologia, from litho- "rock" + -logia "study of" (see -logy). Related: Lithologic; lithologically; lithologist.

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