An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A combining form meaning "race, culture, people."

From Gk. ethnos "people, nation, class, tribe."

Qowm- loan from Ar. qaum "people, tribe, family."

The study of the beliefs, interpretations, and practices of specific cultures regarding celestial objects or phenomena. Ethnoastronomy uses the tools and methodologies of → ethnology in the study of astronomical conceptions.

→ ethno-; → astronomy.

The study of specific cultures (ethnic groups) in their different aspects (anthropological, social, cultural, etc.) to establish similarities and disparities between them.

→ ethno-; → logy.

A chemical group, C₂H₅, produced by removing a hydrogen atom from → ethane. For example, ethyl chloride is C₂H₅Cl

From Ger. Ethyl, from eth-, from → ether, + -yl a suffixed used in the names of radicals.

Same as → ethanol.

→ ethyl; → alcohol.

The study of the origins and history of the form and meaning of → words.

M.E., from L. etymologia, from Gk. etymologia, from etymon "true sense" (neuter of etymos) + logos, → -logy.

Riše-šenâsi, from rišé "root" (dialectal Tabari rexa; Kurd. regez, riše), from Mid.Pers. rêšak "root," maybe ultimately related to PIE *u(e)rad-, although the Skt. offshoot is absent (Gk. rhiza "root;" L. radix, radius "staff;" O.H.G. wurz "plant, herb;" Ger. Wurz; O.E. rot; E. root) + -šenâsi, → -logy.

A prefix meaning "good, well; true, genuine" (eupepsia; eukaryote); opposed to → dys-.

L. from Gk. eu "well," combining form of eus "good" (hu-gies "healthy"); cf. Mid.Pers. hu-; Av. hu- "good;" PIE base *su- "good," see below.

Mid.Pers. hu- "good, well" (hu-boy "sweet-smelling," hu-cihr "beautiful," hu-mânih "good-mindedness"); O.Pers. ^hu- "good, well" (ukāra- "having good people"); Av. hu-, hū- "well, good, beautiful" (hu-kərp- "well-shapen," hūxta- "well spoken," hu-manah- "good-minded"); Skt. su- "good" (svasti "well-being, good luck," sumánas- "good-minded," sūktá- "well spoken"); Gallic su-; O.S. su-; Welsh hy-; PIE base *su-, as above.

Of or pertaining to Euclid, or his postulates. → Euclidean division, → Euclidean geometry, → Euclidean space, → non-Euclidean geometry.

After the Gk. geometrician and educator at Alexandria, around 300 B.C., who applied the deductive principles of logic to geometry, thereby deriving statements from clearly defined axioms.

In arithmetic, the conventional process of division of two → integers. For a → real number a divided by b > 0, there exists a unique integer q and a real number r, 0 ≤ r <b, such that a = qb + r.

→ Euclidean; → division.

The geometry based on the postulates or descriptions of Euclid. One of the critical assumptions of the Euclidean geometry is given in his fifth postulate: through a point not on a line, one and only one line be drawn parallel to the given line. See also → non-Euclidean geometry.

→ Euclidean; → geometry.

A space in which the → distance between any two points is given by the → Pythagorean theorem: d² = (Δx)² + (Δy)² + (Δz)², where d is distance and Δx, Δy, and Δz are differential → Cartesian coordinates. Euclidean n-space Rⁿ is the set of all column vectors with n real entries.

→ Euclidean; → space.

→ spheres of Eudoxus.

→ spheres of Eudoxus.

Leonhard Euler (1707-1783), the eminent Swiss mathematician, physicist, and astronomer.

In → fluid mechanics, one of a set of → differential equations that govern the motion of a → compressible, → inviscid fluid. Euler equations correspond to the → Navier-Stokes equations with zero → viscosity.

→ Euler; → equation.

In any → triangle, the straight line on which always lie the → centroid, → circumcenter, and → orthocenter.

→ Euler; → line.

The line drawn in a coordinate plane connecting the approximate values of the solution of a → first-order differential equation.

→ Euler; → broken line.

A formula which expresses an → exponential function with an → imaginary number  → exponent in terms of → trigonometric functions:
e^iθ = cos θ + i sinθ,
e^-iθ = cos θ - i sinθ,
cosθ = (e^iθ + e^-iθ)/2,
sinθ = (e^iθ - e^-iθ)/2i.
In the particular case of θ = π, Euler's formula becomes: e^iπ + 1 = 0, which is considered by many mathematicians to be the most elegant mathematical equation. → mathematical elegance.

→ Euler; → formula.

Fluid mechanics: A method in which the changes in the physical properties of the fluid, such as velocity, acceleration, and density are described at a fixed point in space occupied by the fluid. Compare with → Lagrangian method.

→ Euler; → method.

An inoffensive word or phrase substituted for one considered offensive or hurtful, especially one concerned with religion, sex, death, or excreta (TheFreeDictionary.com).

From Gk. euphemismos, from euphemizein "speak with fair words, use words of good omen," from → eu- "well," + pheme "speech, voice, talk," from phanai "to speak," ultimately from PIE *bha- "to speak, tell, say;" cf. Skt. bhanati "speaks;" L. fari "to say," fabula "tale, story," fama "talk, rumor, report; reputation;" Armenian ban, bay "word, term."

Xošguyi, xošzabâni, literally "pleasant talking, ~ speach," from xoš "well, pleasant," → eu- + guyi verbal noun of goftan "to say, talk, speak," → logic; zabâni, from zabân, → language.

The → continents of → Europe and → Asia considered as a whole.

From Euro-, → Europe, + → Asia.