Etymology: Originally (in α. forms) < classical Latin atomus (see below). Subsequently (in β. forms) < Middle French athome, atome, etc. (French atome ) particle incapable of further division (2nd half of the 13th cent. in Old French), particle of dust rendered visible by light (1510 as antome ), small particle, grain (1535) and its etymon classical Latin atomus particle incapable of further division, atom, in post-classical Latin also brief moment, twinkling of an eye (Vetus Latina, early 3rd cent. in Tertullian), smallest medieval measure of time (13th cent. in a British source), particle of dust rendered visible by light (7th cent.; 1538 in a British source; compare quot. 1538 at sense 7) < ancient Greek ἄτομος particle incapable of further division, atom, twinkling of an eye, use as noun (partly short for ἄτομος ϕύσις indivisible substance, and partly short for ἄτομος χρόνος indivisible time) of ἄτομος (adjective) indivisible < ἀ- a- prefix⁶ + -τομος (see -tome comb. form); compare ἄτομον, use as noun (short for ἄτομον σῶμα indivisible body) of neuter of ἄτομος. Compare Spanish átomo (1348), Portuguese átomo (15th cent.), Italian atomo (late 14th cent.).Sense 1 is apparently not paralleled in French until considerably later (late 15th or early 16th cent. as antonne , antomne ; also as atomos (1530)). The sense ‘brief moment, twinkling of an eye’ is found for ancient Greek ἄτομος and post-classical Latin atomus in the New Testament, 1 Corinthians 15:52, in the phrase ἐν ἀτόμῳ , in atomo in a moment (Vetus Latina; the Vulgate has in momento ). In the medieval period, post-classical Latin atomus denoted a specific measure of time: there were 376 ‘atoms’ in an ostent, the ostent being equivalent to a modern minute (see Du Cange). In Old English used with Latin case inflections (compare quots. OE¹, OE² at sense 1). Compare also the Middle English plural form attomos in quot. a1398 at sense 1, with Latin accusative plural ending.

Etymology: < atom n. Compare earlier atomed adj.