Etymology
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duty (n.)

late 14c., duete, "obligatory service, that which ought to be done," also "the force of that which is morally right," from Anglo-French duete, from Old French deu "due, owed," hence "proper, just" (on the notion of "that which one is bound by natural, moral, or legal obligation to do or perform"); from Vulgar Latin *debutus, from Latin debitus, past participle of debere "to owe," originally, "keep something away from someone," from de- "away" (see de-) + habere "to have" (from PIE root *ghabh- "to give or receive"). Related: Duties.

Military sense of "a requisite service" is by 1580s. The sense of "tax or fee on imports, exports, etc." is from late 14c.; hence duty-free (adv.) "free from tax or duty" (1680s), and, as a noun, "duty-free article" (1958), "duty-free shop" (by 1980).

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heavy-duty (adj.)
"durable, strong," 1903; see heavy (adj.) + duty.
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off-duty (adj.)

"not employed or occupied with one's normal work," 1743, from off (prep.) + duty.

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dutiable (adj.)

"subject to a customs duty," 1774, from duty + -able.

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dutiful (adj.)

"performing the duties required by social or legal obligation; obediently respectful," 1550s, from duty + -ful. Related: Dutifully; dutifulness. Shakespeare uses duteous.

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inofficious (adj.)
c. 1600, "neglecting one's duty;" in law, "not in accord with one's moral duty," 1660s, from Medieval Latin inofficiosus "contrary to duty; harmful," from in- "not, opposite of" (see in- (1) + Latin officiosus "dutiful, obliging" (see officious).
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defaulter (n.)

"one who fails to perform some duty or obligation," 1650s, agent noun from default (v.).

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endeavor (n.)
early 15c., "pains taken to attain an object," literally "in duty," from phrase put (oneself) in dever "make it one's duty" (a partial translation of Old French mettre en deveir "put in duty"), from Old French dever "duty," from Latin debere "to owe," originally, "keep something away from someone," from de- "away" (see de-) + habere "to have" (from PIE root *ghabh- "to give or receive"). One's endeavors meaning one's "utmost effort" is from late 15c.
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expenses (n.)
"charges incurred in the discharge of duty," late 14c. See expense (n.).
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tonnage (n.)
early 15c., "tax or duty on wine imported in tuns," from ton (n.1) + -age, and from Old French tonnage "duty levied on wine in casks" (c. 1300). Meaning "carrying capacity of a ship" is from 1718.
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