heart-strings (n.)youdaoicibaDictYouDict[heart-strings 词源字典]
also heartstrings, late 15c., in old anatomy, "the tendons and nerves that brace the heart;" from heart (n.) + string (n.). Transferred and figurative sense "strongest affections, most intense feelings" is from 1590s.[heart-strings etymology, heart-strings origin, 英语词源]
literally (adv.)youdaoicibaDictYouDict
1530s, "in a literal sense," from literal + -ly (2). Erroneously used in reference to metaphors, hyperbole, etc., even by writers like Dryden and Pope, to indicate "what follows must be taken in the strongest admissible sense" (1680s), which is opposite to the word's real meaning and a long step down the path to the modern misuse of it.
We have come to such a pass with this emphasizer that where the truth would require us to insert with a strong expression 'not literally, of course, but in a manner of speaking', we do not hesitate to insert the very word we ought to be at pains to repudiate; ... such false coin makes honest traffic in words impossible. [Fowler, 1924]
potent (adj.)youdaoicibaDictYouDict
early 15c., from Latin potentem (nominative potens) "powerful," present participle of *potere "be powerful," from potis "powerful, able, capable; possible;" of persons, "better, preferable; chief, principal; strongest, foremost," from PIE root *poti- "powerful, lord" (cognates: Sanskrit patih "master, husband," Greek posis, Lithuanian patis "husband"). Meaning "having sexual power" is first recorded 1899.
ThoryoudaoicibaDictYouDict
Odin's eldest son, strongest of the gods though not the wisest, c.1020, from Old Norse Þorr, literally "thunder," from *þunroz, related to Old English þunor (see thunder (n.)). His weapon was the hammer mjölnir ("crusher").
XyoudaoicibaDictYouDict
The entire entry for X in Johnson's dictionary (1756) is: "X is a letter, which, though found in Saxon words, begins no word in the English language." Most English words beginning in -x- are of Greek origin or modern commercial coinages. East Anglian in 14c. showed a tendency to use -x- for initial sh-, sch- (such as xal for shall), which didn't catch on but seems an improvement over the current system. As a symbol of a kiss on a letter, etc., it is recorded from 1765. In malt liquor, XX denoted "double quality" and XXX "strongest quality" (1827).

Algebraic meaning "unknown quantity" (1660 in English, from French), sometimes is said to be from medieval use, originally a crossed -r-, in that case probably from Latin radix (see root (n.)). Other theories trace it to Arabic (Klein), but a more prosaic explanation says Descartes (1637) took x, y, z, the last three letters of the alphabet, for unknowns to correspond to a, b, c, used for known quantities.

Used allusively for "unknown person" from 1797, "something unknown" since 1859. As a type of chromosome, attested from 1902 (first so called in German; Henking, 1891). To designate "films deemed suitable for adults only," first used 1950 in Britain; adopted in U.S. Nov. 1, 1968. The XYZ Affair in American history (1797) involved French agents designated by those letters.