ill (adj.)

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.

ill (v.)

early 13c., "do evil to," from ill (adj.). Meaning "speak disparagingly" is from 1520s. Related: Illed; illing.

ill (adv.)

c. 1200, "wickedly; with hostility," from ill (adj.). Meaning "not well, poorly" also is from c. 1200. It generally has not shifted to the realm of physical sickness, as the adjective has done. Ill-fated recorded from 1710; ill-informed from 1824; ill-tempered from c. 1600; ill-starred from c. 1600. Generally contrasted with well, hence the useful, but now obsolete or obscure illcome (1570s), illfare (c. 1300), and illth.

Definitions of ill
ill (adj.)
resulting in suffering or adversity;
it's an ill wind that blows no good
ill effects
ill (adj.)
affected by an impairment of normal physical or mental function;
ill from the monotony of his suffering
Synonyms: sick
ill (adj.)
of ill repute
ill manners
ill (adj.)
indicating hostility or enmity;
you certainly did me an ill turn
ill feelings
ill (adj.)
presaging ill fortune; "my words with inauspicious thunderings shook heaven"- P.B.Shelley;
ill predictions
ill omens
Synonyms: inauspicious / ominous
ill (adv.)
(`ill' is often used as a combining form) in a poor or improper or unsatisfactory manner; not well;
it ill befits a man to betray old friends
ill-fitting clothes
an ill-conceived plan
he was ill prepared
Synonyms: badly / poorly
ill (adv.)
unfavorably or with disapproval;
tried not to speak ill of the dead
Synonyms: badly
ill (adv.)
with difficulty or inconvenience; scarcely or hardly;
we can ill afford to buy a new car just now
ill (n.)
an often persistent bodily disorder or disease; a cause for complaining;
Synonyms: ailment / complaint