Etymology
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galvanometer (n.)
instrument for detecting and measuring electric current, 1801, from galvano-, used as a combining form of galvanism + -meter. Related: Galvanometric. Galvanoscope "instrument for detecting and determining the direction of electric current" is from 1832.
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radar (n.)

"electronic system for locating and tracking objects at a distance by means of radio waves," 1941, acronym (more or less) from radio detecting and ranging. The U.S. choice, it won out over British radiolocation. Figurative from 1950.

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detect (v.)

early 15c., "uncover, lay bare, expose, disclose, reveal," a sense now obsolete, from Latin detectus, past participle of detegere "uncover, expose," figuratively "discover, reveal, disclose," from de "un-, off" (see de-) + tegere "to cover," from PIE root *(s)teg- "to cover."

Sense of "to find out the secret action or character of" is from 1580s. Meaning "discover, find out, ascertain" is from 1756. Related: Detected; detecting.

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detective (n.)

"one whose occupation is to investigate matters as to which information is desired, especially concerning wrong-doers, and to obtain evidence against them," 1828, short for detective police, from detective (adj.) "fitted for or skilled in detecting" (by 1828); see detect + -ive.

His duties differ from those of the ordinary policeman in that he has no specific beat or round, and in that he is concerned with the investigation of specific cases, or the watching of particular individuals or classes of offenders, rather than with the general guardianship of the peace, and does not wear a distinguishing uniform. [Century Dictionary, 1897]
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police (n.)
Origin and meaning of police

1530s, "the regulation and control of a community" (similar in sense to policy (n.1)); from Middle French police "organized government, civil administration" (late 15c.), from Latin politia "civil administration," from Greek polis "city" (see polis).

Until mid-19c. used in England for "civil administration;" application to "administration of public order, law-enforcement in a community" (1716) is from French (late 17c.), and originally in English referred to France or other foreign nations.

The sense of "an organized civil force for maintaining order, preventing and detecting crime, etc." is by 1800; the first force so-named in England was the Marine Police, set up 1798 to protect merchandise at the Port of London. Meaning "body of officers entrusted with the duty of enforcing laws, detecting crime, etc." is from 1810.

In its most common acceptation, the police signifies the administration of the municipal laws and regulations of a city or incorporated town or borough by a corps of administrative or executive officers, with the necessary magistrates for the immediate use of force in compelling obedience and punishing violation of the laws, as distinguished from judicial remedies by action, etc. The primary object of the police system is the prevention of crime and the pursuit of offenders; but it is also subservient to other purposes, such as the suppression of mendicancy, the preservation of order, the removal of obstructions and nuisances, and the enforcing of those local and general laws which relate to the public health, order, safety, and comfort. [Century Dictionary, 1895]

In constitutional law, police power is the power of a government to limit civil liberties and exercise restraint and compulsion over private rights, especially to advance or protect the public welfare. Police state "state regulated by means of national police" first recorded 1865, with reference to Austria. Police action in the international sense of "military intervention short of war, ostensibly to correct lawlessness" is from 1933. Police officer is attested from 1794, American English. Police station is from 1817. Police dog is by 1908.

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check (n.1)

c. 1300, in chess, "a call noting one's move has placed his opponent's king (or another major piece) in immediate peril," from Old French eschequier "a check at chess" (also "chess board, chess set"), from eschec "the game of chess; chessboard; check; checkmate," from Vulgar Latin *scaccus, from Arabic shah, from Persian shah "king," the principal piece in a chess game (see shah; also compare checkmate (n.)). Also c. 1300 in a generalized sense, "harmful incident or event, hostile environment."

As "an exposure of the king to a direct attack from an opposing piece" early 15c. When his king is in check, a player's choices are severely limited. From that notion come the many extended senses: From the notion of "a sudden stoppage, hindrance, restraint" (1510s) comes that of "act or means of checking or restraining," also "means of detecting or exposing or preventing error; a check against forgery or alteration.

"Hence: "a counter-register as a token of ownership used to check against, and prevent, loss or theft" (as in hat check, etc.), 1812.  Hence also the financial use for "written order for money drawn on a bank, money draft" (1798, often spelled cheque), which was probably influenced by exchequer. Hence also "mark put against names or items on a list indicating they have been verified or otherwise examined" (by 1856).

From its use in chess the word has been widely transferred in French and English. In the sense-extension, the sb. and vb. have acted and reacted on each other, so that it is difficult to trace and exhibit the order in which special senses arose [OED]

Meaning "restaurant bill" is from 1869. Checking account is attested from 1897, American English. Blank check in the figurative sense is attested by 1849 (compare carte blanche). Checks and balances is from 1782, perhaps originally suggesting machinery.

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