earnest (adj.1)youdaoicibaDictYouDict[earnest 词源字典]
from Old English eornoste (adj.) "zealous, serious," or from Old English noun eornost "seriousness, serious intent" (surviving only in the phrase in earnest), from Proto-Germanic *er-n-os-ti- (cognates: Old Saxon ernust, Old Frisian ernst, Old High German arnust "seriousness, firmness, struggle," German Ernst "seriousness;" Gothic arniba "safely, securely;" Old Norse ern "able, vigorous," jarna "fight, combat"), perhaps from PIE root *er- (1) "to move, set in motion." The proper name Ernest (literally "resolute") is from the same root. Related: Earnestness.[earnest etymology, earnest origin, 英语词源]
fast (adv.)youdaoicibaDictYouDict
Old English fæste "firmly, securely; strictly;" also, perhaps, "speedily," from Proto-Germanic *fasto (cognates: Old Saxon fasto, Old Frisian feste, Dutch vast, Old High German fasto, German fast "firmly, immovably, strongly, very"), from *fastu- (adj.) "firm, fast" (see fast (adj.)).

The meaning "quickly, swiftly, rapidly" was perhaps in Old English, certainly by c. 1200, probably from or developed under influence of Old Norse fast "firmly, fast." This sense developed, apparently in Scandinavian, from that of "firmly, strongly, vigorously" (to run hard means the same as to run fast; also compare fast asleep, also compare Old Norse drekka fast "to drink hard," telja fast "to give (someone) a severe lesson"). Or perhaps from the notion of a runner who "sticks" close to whatever he is chasing (compare Old Danish fast "much, swiftly, at once, near to, almost," and sense evolution of German fix "fast, fixed; fast, quick, nimble," from Latin fixus). The expression fast by "near, close, beside" also is said to be from Scandinavian. To fast talk someone (v.) is recorded by 1946.
fixture (n.)youdaoicibaDictYouDict
1590s, "act of fixing," perhaps from fix (v.) on model of mixture, or from an assumed Latin *fixitatem. Meaning "anything fixed or securely fastened" is from 1812, an alteration of fixure (c. 1600).
insecure (adj.)youdaoicibaDictYouDict
1640s, "unsafe," from Medieval Latin insecurus, from in- "not" (see in- (1)) + Latin securus (see secure). Psychological sense dates from 1935; insecurity in this sense dates from 1917. Related: Insecurely.
loose (adj.)youdaoicibaDictYouDict
early 13c., "not securely fixed;" c. 1300, "unbound," from Old Norse lauss "loose, free, vacant, dissolute," cognate with Old English leas "devoid of, false, feigned, incorrect," from Proto-Germanic *lausaz (cognates: Danish løs "loose, untied," Swedish lös "loose, movable, detached," Middle Dutch, German los "loose, free," Gothic laus "empty, vain"), from PIE *leu- "to loosen, divide, cut apart" (see lose). Meaning "not clinging, slack" is mid-15c. Meaning "not bundled" is late 15c. Sense of "unchaste, immoral" is recorded from late 15c. Meaning "at liberty, free from obligation" is 1550s. Sense of "rambling, disconnected" is from 1680s. Figurative sense of loose cannon was in use by 1896, probably from celebrated image in a popular story by Hugo:
You can reason with a bull dog, astonish a bull, fascinate a boa, frighten a tiger, soften a lion; no resource with such a monster as a loose cannon. You cannot kill it, it is dead; and at the same time it lives. It lives with a sinister life which comes from the infinite. It is moved by the ship, which is moved by the sea, which is moved by the wind. This exterminator is a plaything. [Victor Hugo, "Ninety Three"]
Loose end in reference to something unfinished, undecided, unguarded is from 1540s; to be at loose ends is from 1807. Phrase on the loose "free, unrestrained" is from 1749 (upon the loose).
secure (adj.)youdaoicibaDictYouDict
1530s, "without care, dreading no evil," from Latin securus, of persons, "free from care, quiet, easy," also in a bad sense, "careless, reckless;" of things, "tranquil; free from danger, safe," from *se cura, from se "free from" (see secret (n.1)) + cura "care" (see cure (n.)).

In English, of places, "free from danger, unexposed," from 1580s. Meaning "firmly fixed" (of material things) is from 1841, on notion of "affording grounds for confidence." Of telephones, "not wiretapped," from 1961. Replaced Middle English siker, from Old English sicor, from the Latin word. Related: Securely.
solidly (adv.)youdaoicibaDictYouDict
1610s, "firmly, securely," from solid (adj.) + -ly (2). Meaning "unanimously" is from 1865, American English.