ekluō

ἐκλύω is ἐκ- ("out of, completely") + λύω ("to loosen"), and its history runs from the literal (unstringing a bow, Herodotus 2.173; dissolving a quarrel, Demosthenes 19.224) to the passive "become slack, grow faint." The moral-psychological sense is already attested in classical Attic prose (Isocrates 4.150; Aristotle fr. 144), but its center of gravity shifted under Polybius, whose military prose repeatedly pairs the verb with the dative ταῖς ψυχαῖς for demoralized troops (20.4.7; 29.6.14), and decisively under the Septuagint, which used ἐκλύω to render a cluster of Hebrew slackness verbs (רָפָה, מָסַס, מוּג, עָיֵף) and fixed the idiom μὴ ἐκλυέσθω ἡ καρδία of Deuteronomy 20:3. Louw-Nida sorts the New Testament uses into physical weariness (§23.79: Matt 15:32; Mark 8:3) and discouragement (§25.288: Gal 6:9; Heb 12:3, 5), and commentators are essentially unanimous that the Gospel uses are bodily and the Pauline and Hebrews uses moral. In Hebrews 12:3 the dative ταῖς ψυχαῖς is generally construed with ἐκλυόμενοι, and the choice of the verb anticipates the verbatim quotation of Proverbs 3:11 LXX in 12:5, where the translator had already rendered Hebrew קוץ ("loathe") interpretively as ἐκλύου ("lose heart"). One live debate, over Galatians 6:9, is grammatical rather than lexical: whether μὴ ἐκλυόμενοι is conditional ("if we do not give up," the modern consensus) or adverbial ("we will reap unwearyingly," argued by Jensen 2018 and matching the patristic reading); the sense of the verb is unaffected either way. A related caution: the KJV "faint not" of 2 Corinthians 4:1, 16 renders ἐγκακέω, not this verb, so the English overlap is translational, not textual.