英语词源字典 - 在线词源网站

facilis descensus Averni [facilis descensus Averni 词源字典]: Latin, literally "the descent of Avernus (is) easy" ["Aeneid," VI.126], in reference to Avernus, a deep lake near Puteoli and a reputed entrance to the underworld; hence, "it is easy to slip into moral ruin."[facilis descensus Averni etymology, facilis descensus Averni origin, 英语词源]
sleeve (n.): Old English sliefe (West Saxon), slefe (Mercian) "arm-covering part of a garment," probably literally "that into which the arm slips," from Proto-Germanic *slaubjon (cognates: Middle Low German sloven "to dress carelessly," Old High German sloufen "to put on or off"). Related to Old English slefan, sliefan "to slip on (clothes)" and slupan "to slip, glide," from PIE root *sleubh- "to slide, slip."

Compare slipper, Old English slefescoh "slipper," slip (n.2) "woman's garment," and expression slip into "dress in." Mechanical sense is attested from 1864. Meaning "the English Channel" translates French La Manche. To have something up one's sleeve is recorded from c. 1500 (large sleeves formerly doubled as pockets). To wear one's heart on (one's) sleeve is from "Othello" (1604).
smug (adj.): 1550s, "trim, neat, spruce, smart," possibly an alteration of Low German smuk "trim, neat," from Middle Low German smücken "to adorn" (originally "to dress," secondary sense of words meaning "to creep or slip into"), from the same source as smock. The meaning "having a self-satisfied air" is from 1701, an extension of the sense of "smooth, sleek" (1580s), which was commonly used of attractive women and girls. Related: Smugly; smugness.