theoretical (adj.)
1610s, "contemplative," with -al (1) + Late Latin theoreticus "of or pertaining to theory," from Greek theoretikos "contemplative, speculative, pertaining to theory" (by Aristotle contrasted to praktikos), from theoretos "that may be seen or considered," from theorein "to consider, look at" (see theory). Meaning "pertaining to theory, making deductions from theory not from fact" (opposed to practical) is from 1650s; earlier in this sense was theorical (c. 1500). Meaning "ideal, hypothetical" is from 1790s (implied in theoretically). Related: theoretician.
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science (n.)
Origin and meaning of science

mid-14c., "state or fact of knowing; what is known, knowledge (of something) acquired by study; information;" also "assurance of knowledge, certitude, certainty," from Old French science "knowledge, learning, application; corpus of human knowledge" (12c.), from Latin scientia "knowledge, a knowing; expertness," from sciens (genitive scientis) "intelligent, skilled," present participle of scire "to know."

The original notion in the Latin verb probably is "to separate one thing from another, to distinguish," or else "to incise." This is related to scindere "to cut, divide" (from PIE root *skei- "to cut, split;" source also of Greek skhizein "to split, rend, cleave," Gothic skaidan, Old English sceadan "to divide, separate").

OED writes that the oldest English sense of the word now is restricted to theology and philosophy. From late 14c. in English as "book-learning," also "a particular branch of knowledge or of learning, systematized knowledge regarding a particular group of objects;" also "skillfulness, cleverness; craftiness." From c. 1400 as "experiential knowledge;" also "a skill resulting from training, handicraft; a trade."

From late 14c. in the more specific sense of "collective human knowledge," especially that gained by systematic observation, experiment, and reasoning. The modern (restricted) sense of "body of regular or methodical observations or propositions concerning a particular subject or speculation" is attested by 1725; in 17c.-18c. this commonly was philosophy.

The sense of "non-arts studies" is attested from 1670s. The distinction is commonly understood as between theoretical truth (Greek epistemē) and methods for effecting practical results (tekhnē), but science sometimes is used for practical applications and art for applications of skill.

The predominant modern use, "natural and physical science," generally restricted to study of the phenomena of the material universe and its laws, is by mid-19c.

To blind (someone) with science "confuse by the use of big words or complex explanations" is attested from 1937, originally noted as a phrase from Australia and New Zealand. 

The men who founded modern science had two merits which are not necessarily found together: Immense patience in observation, and great boldness in framing hypotheses. The second of these merits had belonged to the earliest Greek philosophers; the first existed, to a considerable degree, in the later astronomers of antiquity. But no one among the ancients, except perhaps Aristarchus, possessed both merits, and no one in the Middle Ages possessed either. [Bertrand Russell, "A History of Western Philosophy," 1945] 
Science, since people must do it, is a socially embedded activity. It progresses by hunch, vision, and intuition. Much of its change through time does not record a closer approach to absolute truth, but the alteration of cultural contexts that influence it so strongly. Facts are not pure and unsullied bits of information; culture also influences what we see and how we see it. Theories, moreover, are not inexorable inductions from facts. The most creative theories are often imaginative visions imposed upon facts; the source of imagination is also strongly cultural. [Stephen Jay Gould, introduction to "The Mismeasure of Man," 1981]
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science fiction (n.)

1929 (in advertisements for "Air Wonder Stories" magazine), though there is an isolated use from 1851. See science + fiction. Earlier in same sense was scientifiction (by 1926). Abbreviated form sci-fi is by 1955. 

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pseudo-science (n.)

also pseudoscience, "a pretended or mistaken science," 1796 (the earliest reference is to alchemy), from pseudo- + science.

The term pseudo-science is hybrid, and therefore objectionable. Pseudognosy would be better etymology, but the unlearned might be apt to association with it the idea of a dog's nose, and thus, instead of taking "the eel of science by the tail," take the cur of science by the snout; so that all things considered we had better adopt the current term pseudo-sciences ["The Pseudo-Sciences," in The St. James's Magazine, January 1842]
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mathematics (n.)

"the science of quantity; the abstract science which investigates the concepts of numerical and spatial relations," 1580s; see mathematic (the older form of the word in English, attested from late 14c.) + -ics. Originally one of three branches of Aristotelian theoretical science, along with first philosophy (or metaphysics) and physics (or natural philosophy).

Mystical doctrines as to the relation of time to eternity are also reinforced by pure mathematics, for mathematical objects, such as numbers, if real at all, are eternal and not in time. Such eternal objects can be conceived as God's thoughts. [Bertrand Russell, "A History of Western Philosophy"]
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practic (n.)

late 14c., practike, "practical aspect of doing something, method; practice (as opposed to theory), practical knowledge or experience;" also "an applied science;" from Old French practique "practice, usage" (13c.) and directly from Medieval Latin practica "accomplishment, practical knowledge," ultimately from Greek praktikē "of or pertaining to actions, concerned with action or business"(as opposed to "theoretical"); fem. of praktikos "done; to be done" (see practical).

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applied (adj.)
"put to practical use," (as opposed to abstract or theoretical), 1650s, from past participle of apply. Earlier it was used in a sense of "folded" (c. 1500).
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global warming (n.)
by 1983 as the name for a condition of overall rising temperatures on Earth and attendant consequences as a result of human activity. Originally theoretical, popularized as a reality from 1989.
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Einstein (n.)
as a type-name for a person of genius, 1920, in reference to German-born theoretical physicist Albert Einstein (1879-1955), who was world-famous from 1919 through media accounts of his work in theoretical physics. According to "German-American Names" (George F. Jones, 3rd ed., 2006) it means literally "place encompassed by a stone wall."
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physics (n.)

1580s, "natural science, the science of the principles operative in organic nature," from physic in sense of "natural science." Also see -ics. Based on Latin physica (neuter plural), from Greek ta physika, literally "the natural things," title of Aristotle's treatise on nature. The current restricted sense of "science treating of properties of matter and energy" is from 1715.

Before the rise of modern science, physics was usually defined as the science of that which is movable, or the science of natural bodies. It was commonly made to include all natural science. At present, vital phenomena are not considered objects of physics, which is divided into general and applied physics. [Century Dictionary, 1895]
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