An Etymological Dictionary of Astronomy and Astrophysics
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Newton's third law of motion, which states that for every action there must be an equal and opposite reaction.

→ principle; → action; → reaction.

The second postulate in Einstein's theory of → special relativity whereby the → velocity of light in → vacuum has the same absolute value in all → inertial reference frames irrespective of the direction and speed of propagation of the light source. It should be emphasized that this constancy of the speed of light holds among → reference frames moving uniformly with respect to each other. An observer accelerated with respect to a light source will measure a speed of light that is smaller than the speed of light measured in a → rest frame. See also → principle of relativity.

→ principle; constancy, noun related to → constant.

In special relativity, the principle that the laws of physics take the same mathematical form in all inertial frames of reference.

→ principle; → covariance.

In → general relativity the principle which states that in the immediate proximity of an → accelerating system the acceleration is physically equivalent to → gravitational force. This principle also implies the equivalence of → gravitational mass and → inertial mass. Same as the → equivalence principle. See also → Einstein's elevator.

→ principle; → equivalence.

The second principle of → formal logic introduced in Aristotle's theory of the → syllogism: A statement is either → true or → false. In other words, two → contradictory → propositions cannot both be true. The truth of one implies the falsehood of the other. Also called law of excluded middle and → principle of excluded third.

→ principle; → exclude; → middle.

Same as → principle of excluded middle.

→ principle; → exclude; → third.

The first principle of → formal logic introduced in Aristotle's theory of the → syllogism: If a statement is true then it is true. Also called → law of identity.

→ principle; → identity.

The principle that, for a system whose total mechanical energy is conserved, the path to be taken for the system from one configuration to another is the one whose action has the least value relative to all other possible paths and from the same configurations. Also called Maupertuis' principle, least-action principle.

→ principle; → least; → action.

The third principle of → formal logic introduced in Aristotle's theory of the → syllogism: No statement can be both → true and → false at the same time. Also called → law of non-contradiction.

→ principle; → non-; → contradiction.

One consequence of the theory of → special relativity, according to which no two events separated by a distance greater than their separation in time multiplied by the → speed of light may have a → causal influence on each other. Violation of this principle leads to → paradoxes, such as that of an → effect preceding its → cause.

→ principle; → relativistic; → causality.

The first postulate in Einstein's theory of → special relativity whereby all the laws of physics are the same in every → inertial reference frame. In other words, no physical measurement can distinguish one inertial reference frame from another. See also → principle of constancy.

→ principle; → relativity.

1a) The state of being printed.
1b) Printed lettering, especially with reference to character, style, or size.
1c) Printed material; a printed publication, as a newspaper or magazine.
2a) To produce (a text, picture, etc.) by applying inked types, plates, blocks, or the like, to paper or other material either by direct pressure or indirectly by offsetting an image onto an intermediate roller.
2b) To reproduce (a design or pattern) by engraving on a plate or block.
2c) To form a design or pattern upon, as by stamping with an engraved plate or block.
2d) To cause (a manuscript, text, etc.) to be published in print (Dictionary.com).

M.E. prent(e), print(e), prient(e), from OF priente "impression," noun use of feminine p.p. of preindre "to press," from L. premere "to press, hold fast."

Câp "press," loan from Indo-Aryan languages chapa, chháp, chāp "seal, stamp, impression."

1) A person or thing that prints, especially a person whose occupation is printing.
2) Computers: An output device that produces a paper copy of alphanumeric or graphic data (Dictionary.com).

→ print; → -er.

A font used for printing. See also → screen font.

→ printer; → font.

1) Preceding in time or in order; earlier or former; previous.
2) Preceding in importance or privilege.

O.E., from M.L. prior "former, previous, first, superior," comparative of O.L. pri "before," from PIE *prai-, *prei-, from root *per- "forward, through," → pro-.

Parin, from pra-, fra- "before, forward, forth," cognate with Gk. and L. → pro-.

The condition or quality of being earlier in time or occurrence, or being regarded as more important.

→ prior; → -ity.

Optics: A transparent solid body, having at least two polished plane faces inclined relative to each other, from which light is reflected or through which light is refracted.
Geometry: A solid having two faces lying in parallel planes and with the other faces parallelograms.

L.L. prisma, from Gk. prisma, literally "something sawed," from prizein "to saw."

Manšur, etymology not clear, may be related to Ar. mawšur "prism," of unknown origin.

The angle between the faces on which light is incident and from which it emerges.

→ prism; → angle.

An optical device consisting of a pair of small telescopes mounted side by side, each telescope having two prisms between the eyepiece and objective for erecting the image.

→ prism; → binoculars.

An ocular equipped with a prism that forms an upright image in an astronomical telescope.

→ prism; → ocular.