Etymology
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tough (adj.)
Old English toh "strong and firm in texture, tenacious, sticky," from Proto-Germanic *tanhu- (source also of Middle Low German tege, Middle Dutch taey, Dutch taai, Old High German zach, German zäh), which Watkins suggests is from PIE *denk- "to bite," from the notion of "holding fast." See rough for spelling change.

From c. 1200 as "strong, powerful;" c. 1300 as "not tender or fragile;" early 14c. as "difficult to chew," also "hard to endure." Figurative sense of "steadfast" is mid-14c.; that of "hard to do, trying, laborious" is from 1610s. Verb tough it "endure the experience" is first recorded 1830, American English. Tough guy attested from 1901. Tough-minded first recorded 1907 in William James. Tough luck first recorded 1912; tough shit, dismissive retort to a complaint, is from 1946.
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bond (adj.)
c. 1300, "in a state of a serf, unfree," from bond (n.) "tenant, farmer holding land under a lord in return for customary service; a married bond as head of a household" (mid-13c.). The Old English form was bonda, bunda "husbandman, householder," but the Middle English word probably is from Old Norse *bonda, a contraction of boande, buande "occupier and tiller of soil, peasant, husbandman," a noun from the past participle of bua, boa "to dwell" (from PIE root *bheue- "to be, exist, grow").

"In the more despotic Norway and Denmark, bo'ndi became a word of contempt, denoting the common low people. ... In the Icelandic Commonwealth the word has a good sense, and is often used of the foremost men ...." [OED]. The sense of the noun deteriorated in English after the Conquest and the rise of the feudal system, from "free farmer" to "serf, slave" (c. 1300) and the word became associated with unrelated bond (n.) and bound (adj.1).
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rival (n.)

1570s, "one who is in pursuit of the same object as another;" 1640s, "one who emulates or strives to equal or exceed another" in some way; from Latin rivalis "a rival, adversary in love; neighbor," originally, "of the same brook," from rivus "brook" (from PIE root *rei- "to run, flow").

The sense evolution seems to be based on the competitiveness of neighbors: "one who uses the same stream," or "one on the opposite side of the stream," hence in various ways "one who is in pursuit of the same object or resource as another."

A secondary sense in Latin and sometimes in English was "associate, companion in duty," from the notion of "one having a common right or privilege with another." As an adjective, "having the same pretentions or claims, holding the position of rivals," 1580s, from the noun.

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stay (v.1)
mid-15c., "cease going forward, come to a halt," also (transitive) "detain, hold back," from Old French estai-, stem of estare "to stay or stand," from Latin stare "to stand, stand still, remain standing; be upright, be erect; stand firm, stand in battle; abide; be unmovable; be motionless; remain, tarry, linger; take a side," (source also of Italian stare, Spanish estar "to stand, to be"), from PIE root *sta- "to stand, make or be firm." Sense of "remain" is first recorded 1570s; that of "reside as a guest for a short period" is from 1550s. Related: Stayed; staying.

Of things, "remain in place," 1590s. Stay put is first recorded 1843, American English. "To stay put is to keep still, remain in order. A vulgar expression" [Bartlett]. Phrase stay the course is originally (1885) in reference to horses holding out till the end of a race. Stay-stomach was (1800) "a snack."
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navigation (n.)

1530s, "act of moving on water in ships or other vessels," from French navigation (14c.) or directly from Latin navigationem (nominative navigatio) "a sailing, navigation, voyage," noun of action from past-participle stem of navigare "to sail, sail over, go by sea, steer a ship," from navis "ship" (from PIE root *nau- "boat") + root of agere "to set in motion, drive, drive forward" (from PIE root *ag- "to drive, draw out or forth, move"). Meaning "science or art of directing the course of vessels as they sail" is from 1550s.

The management of the sails, etc., the holding of the assigned course by proper steering, and the working of the ship generally pertain rather to seamanship, though necessary to successful navigation. The two fundamental problems of navigation are the determination of the ship's position at a given moment, and the decision of the most advantageous course to be steered in order to reach a given point. [Century Dictionary]
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candle (n.)

"cylindrical body of tallow, wax, etc., formed on a wick and used as a source of artificial light," Old English candel "lamp, lantern, candle," an early ecclesiastical borrowing from Latin candela "a light, torch, candle made of tallow or wax," from candere "to shine," from PIE root *kand- "to shine."

The Latin word is also the source of French chandelle, Spanish candela, Irish coinneal, Welsh canwyll, Russian kandilo, Arabic qandil, etc. Candles were unknown in ancient Greece (where oil lamps sufficed), but common from early times among Romans and Etruscans. Candles on birthday cakes seem to have been originally a German custom. To hold a candle to originally meant "to help in a subordinate capacity," from the notion of an assistant or apprentice holding a candle for light while the master works (compare Old English taporberend "acolyte"). To burn the candle at both ends "consume or waste prodigiously" is recorded from 1730.

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commencement (n.)

late 13c., "a beginning, act or fact of coming into existence," from Old French comencement "beginning, start" (Modern French commencement), from comencier "to begin, to start" (see commence).

Meaning "school graduation ceremony" attested by 1850, American English, originally in colleges, in reference to the ceremonies by which members of the graduating class are made ("begin to be") bachelors, masters, etc. (commencement in the sense of "entrance upon the privileges of a master or doctor in a university" is from late 14c.) ; thence extended to graduation ceremonies of academies and lower schools.

I know what you are thinking of — the class members grouped in a semicircle on the stage, the three scared boys in new ready-made black suits, the seventeen pretty girls in fluffy white dresses (the gowns of the year), each senior holding a ribbon-tied manuscript bulging with thoughts on "Beyond the Alps Lies Italy," "Our Ship is Launched — Whither Shall it Sail?" and similar topics. [Charles Moreau Harger, "The Real Commencement," New Outlook, May 8, 1909]
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handicap (n.)

1650s, from hand in cap, a game whereby two bettors would engage a neutral umpire to determine the odds in an unequal contest. The bettors would put their hands holding forfeit money into a hat or cap. The umpire would announce the odds and the bettors would withdraw their hands — hands full meaning that they accepted the odds and the bet was on, hands empty meaning they did not accept the bet and were willing to forfeit the money. If one forfeited, then the money went to the other. If both agreed either on forfeiting or going ahead with the wager, then the umpire kept the money as payment. The custom, though not the name, is attested from 14c. ("Piers Plowman").

Reference to horse racing is 1754 (Handy-Cap Match), where the umpire decrees the superior horse should carry extra weight as a "handicap;" this led to sense of "encumbrance, disability" first recorded 1890. The main modern sense, "a mental or physical disability," is the last to develop, early 20c.

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bush (n.)

"many-stemmed woody plant," from Old English bysc (found in place names), from West Germanic *busk "bush, thicket" (source also of Old Saxon and Old High German busc, Dutch bosch, bos, German Busch). Influenced by or combined with Old French (busche "firewood") and Medieval Latin busca (source also of Italian bosco, Spanish bosque, French bois), both of which probably are from Germanic (compare Boise).

In the British American colonies, applied from 1650s to the uncleared districts. In South Africa, "country," as opposed to town (1780); probably from Dutch bosch in the same sense. As "branch of a tree hung out as a tavern-sign," 1530s; hence the proverb "good wine needs no bush." Meaning "pubic hair" (especially of a woman) is from 1745. To beat the bushes (mid-15c.) is a way to rouse birds so that they fly into the net which others are holding, which originally was the same thing as beating around the bush (see beat (v.)).

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doublethink (n.)

"power of holding two contradictory beliefs in one's mind simultaneously, and accepting both of them" (Orwell), 1948, coined by George Orwell in "Nineteen Eighty-Four," from double (adj.) + think.

To know and not to know, to be conscious of complete truthfulness while telling carefully constructed lies, to hold simultaneously two opinions which cancelled out, knowing them to be contradictory and believing in both of them, to use logic against logic, to repudiate morality while laying claim to it, to believe that democracy was impossible and that the Party was the guardian of democracy, to forget whatever it was necessary to forget, then to draw it back into memory again at the moment when it was needed, and then promptly to forget it again, and above all, to apply the same process to the process itself—that was the ultimate subtlety: consciously to induce unconsciousness, and then, once again, to become unconscious of the act of hypnosis you had just performed. Even to understand the word—doublethink—involved the use of doublethink. ["Nineteen Eighty-Four"]
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