Entries linking to illness
c. 1200, "morally evil; offensive, objectionable" (other 13c. senses were "malevolent, hurtful, unfortunate, difficult"), from Old Norse illr "evil, bad; hard, difficult; mean, stingy," a word of unknown origin. Not considered to be related to evil. From mid-14c. as "marked by evil intentions; harmful, pernicious." Sense of "sick, unhealthy, diseased, unwell" is first recorded mid-15c., probably from a use similar to that in the Old Norse idiom "it is bad to me." Slang inverted sense of "very good, cool" is 1980s.
word-forming element denoting action, quality, or state, attached to an adjective or past participle to form an abstract noun, from Old English -nes(s), from Proto-Germanic *in-assu- (cognates: Old Saxon -nissi, Middle Dutch -nisse, Dutch -nis, Old High German -nissa, German -nis, Gothic -inassus), from *-in-, originally belonging to the noun stem, + *-assu-, abstract noun suffix, probably from the same root as Latin -tudo (see -tude).