Etymology
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malaise (n.)

c. 1300, maleise "pain, suffering; sorrow, anxiety," also, by late 14c., "disease, sickness," from Old French malaise "difficulty, suffering, hardship," literally "ill-ease," from mal "bad" (see mal-) + aise "ease" (see ease (n.)). The current use, in the sense of "unease, discomfort," especially "an indefinite feeling of uneasiness," is perhaps a mid-18c. reborrowing from Modern French. A Middle English verbal form, malasen "to trouble, distress" (mid-15c.), from Old French malaisier, did not endure.

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*mel- (3)

Proto-Indo-European root meaning "false, bad, wrong." The exact sense of the root remains uncertain, "since it concerns a collection of largely isolated words in different IE branches" [de Vaan].

It forms all or part of: blame; blaspheme; blasphemous; blasphemy; ‌‌dismal; mal-; malady; malaise; malaria; malediction; malefactor; malefic; malevolence; malevolent; malice; malicious; malign; malison; malversation; mauvais.

It is the hypothetical source of/evidence for its existence is provided by: Avestan mairiia‑, "treacherous;" Greek meleos "idle; unhappy;" Latin male (adv.) "badly," malus (adj.) "bad, evil;" Old Irish mell "destruction;" Armenian mel "sin;" Lithuanian melas "lie," Latvian malds "mistake," possbily also Greek blasphemein "to slander." 

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