The lexicons place πικρία on an arc from "sharp, piercing" (its early Homeric use of arrows) through "bitter to the taste" to "harsh, resentful" (LSJ, s.v. πικρός; BDAG 812-13; Louw-Nida 88.201-204; Michaelis, TDNT 6:122-27). New Testament usage of the noun divides into two registers. In the Hellenistic ethical register (Eph 4:31; Rom 3:14) πικρία is the settled temper of resentment familiar from Aristotle's δυσδιάλυτοι, "those hard to reconcile" (Nic. Eth. 4.11.5), and continued through Plutarch and the papyri; the commentators are unanimous here (Hoehner; Best, ICC; Lincoln, WBC; O'Brien, PNTC). In the Septuagintal register (Acts 8:23; Heb 12:15) πικρία draws on LXX Deuteronomy 29:17, where it renders לַעֲנָה (wormwood) and, paired with χολή (for רֹאשׁ), characterizes the covenant apostate "whose heart turns away." Acts 8:23 is a near-citation of that text, placing Simon in the role of the covenant-turncoat (Barrett, ICC; Fitzmyer, AB; Bock, BECNT), and Heb 12:15 alludes to it (Attridge, Hermeneia; Lane, WBC; Ellingworth, NIGTC), with wide agreement that the "root of bitterness" is an apostate whose defection defiles many, not a private grudge; some also cite 1QS 2:11-18 and 1QH ix.16 as showing the passage was a live intertext for community discipline. At Rom 3:14 Paul follows LXX Psalm 9:28, where πικρία renders Hebrew מִרְמוֹת ("deceits"); scholars debate whether this reflects a textual or aural confusion with the מרר root or a deliberate semantic bridge to hostile, biting speech (Cranfield, ICC; Dunn, WBC; Fitzmyer, AB), but all read it as verbal cruelty. Underlying both registers is the LXX's deliberate use of the πικρ- stem across the adjacent Hebrew fields of מרר ("bitter") and מרה ("rebel").