Synonyms for Ill-natured:

adj.

bad-tempered (adjective)
disagreeable, cross, ornery, irritable, crabby, sullen, crotchety, mean, malevolent, malicious, hot-tempered, dyspeptic, surly, sulky, crabbed, catty, churlish, petulant, touchy, ill-humored, spiteful, nasty.
disagreeable (adjective)
pettish.
malevolent (adjective)
bitter, hostile, Black-hearted, corrosive, vicious, malignant, hurtful, antagonistic, rancorous, mean, spiteful, churlish, malicious, treacherous, catty, vindictive, sinister, sullen, malevolent, baleful, baneful, wicked, nasty, virulent, evil, perfidious, foul, venomous, hateful.

n.

cross (noun)
disagreeable.
ill-natured (noun)
fussy, crabby, moody, prickly, gruff, sour, glowering, grouchy, cantankerous, curmudgeonly, churlish, shirty, misogynous, dour, waspish, choleric, ill-tempered, nagging, irritable, saturnine, hotheaded, touchy, glum, bristly, cranky, morose, splenetic, pettish, cross, ill-humored, huffish, liverish, snappish, bilious, snorty, crotchety, snappy, quick-tempered, shrewish, feisty, irascible, short-tempered, spoilt, dark, crabbed, testy, dyspeptic, short, spoiled, techy, bad-tempered, petulant, fractious, ugly, misanthropic, peckish, atrabilious, peevish, crusty, nettlesome, currish, surly, sullen, grumpy, tetchy, ornery, sulky, ill-humoured, hot-tempered, misanthropical.

Other synonyms:

Other relevant words:
hot-tempered, sulky, nettlesome, peckish, curmudgeonly, misogynous, misanthropical, pettish, bristly, fractious, testy, ornery, huffish, crabby, touchy, glum, misanthropic, glowering, atrabilious, bilious, currish, techy, dark, fussy, irritable, dyspeptic, grouchy, quick-tempered, dour, moody, peevish, gruff, snappish, ill-humored, liverish, spoilt, splenetic, grumpy, choleric, ill-humoured, hotheaded, ill-tempered, surly, crabbed, prickly, shirty, saturnine, bad-tempered, short-tempered, tetchy, irascible, crusty, feisty, petulant, ugly, cranky, snorty, disagreeable, short, crotchety, waspish, cross, morose, spoiled, shrewish, cantankerous, sour, snappy, nagging.