"systematic vowel alteration in the root of a word to indicate shades of meaning or tense," a characteristic of Indo-European languages, 1845, from German Ablaut, literally "off-sound" ("off" here denoting substitution), coined by J.P. Zweigel in 1568 from ab "off" (from Old High German aba "off, away from," from PIE root *apo- "off, away") + Laut "sound, tone" (from Old High German hlut, from Proto-Germanic *hludaz "heard, loud," from suffixed form of PIE root *kleu- "to hear"). The word was popularized by Jakob Grimm and Franz Bopp. The process is what makes strong verbs in Germanic. An example is bind/band/bond/bound + (German) Bund. Compare umlaut.

In our language, it seems to us that the uncouthness of such compounds as Upsound, Offsound, and Insound, could hardly be compensated by any advantage to be derived from their use; and we therefore purpose, in the course of this work, where any of these terms occur in the original, to retain them in their German shape. Of these terms, Ablaut and Umlaut are those which chiefly, if not alone, are used by our author. [from footnote in translation of Bopp's "Comparative Grammar," London, 1845]

flattering courtier of Dionysius I, tyrant of Syracuse; his name in Greek means literally "fame of the people," from dēmos, damos "people" (see demotic) + -kles "fame," a common ending in Greek proper names, related to kleos "rumor, report, news; good report, fame, glory," from PIE *klew-yo-, suffixed form of root *kleu- "to hear." To teach Damocles the peril that accompanies a tyrant's pleasures, Dionysius seated him at a banquet with a sword suspended above his head by a single hair. Hence the figurative use of sword of Damocles, by 1747. Related: Damoclean.

Greek hero, son of Zeus and Alcmene, worshipped by the Romans as a god of strength, c. 1200 (originally in reference to the Pillars of Hercules), also Ercules, from Latin Hercles (Etruscan Hercle), from Greek Hērakles, literally "Glory of Hera;" from Hera (q.v.) + -kles "fame," a common ending in Greek proper names, related to kleos "rumor, report, news; good report, fame, glory," from PIE *klew-yo-, suffixed form of root *kleu- "to hear."

Used figuratively in reference to strength since late 14c. Vocative form Hercule was a common Roman interjection (especially me Hercule!) "assuredly, certainly." The constellation so called in English by 1670s.

Old English hlysnan (Northumbrian lysna) "to listen, hear; attend to, obey" (transitive), from Proto-Germanic *hlusinon (source also of Dutch luisteren, Old High German hlosen "to listen," German lauschen "to listen"), from PIE root *kleu- "to hear."

This root is the source also of Sanskrit srnoti "hears," srosati "hears, obeys;" Avestan sraothra "ear;" Middle Persian srod "hearing, sound;" Lithuanian klausau, klausyti "to hear," šlovė "splendor, honor;" Old Church Slavonic slusati "to hear," slava "fame, glory," slovo "word;" Greek klyo "hear, be called," kleos "report, rumor, fame glory," kleio "make famous;" Latin cluere "to hear oneself called, be spoken of;" Old Irish ro-clui-nethar "hears," clunim "I hear," clu "fame, glory," cluada "ears;" Welsh clywaf "I hear;" Old English hlud "loud," hleoðor "tone, tune;" Old High German hlut "sound;" Gothic hiluþ "listening, attention."

The -t- probably is by influence of Old English hlystan (see list (v.2)). For vowel evolution, see bury. Intransitive sense is from c. 1200. To listen in (1905) was originally in reference to radio broadcasts.