"what leads one to a bad state or condition," 1867, coined by John Ruskin from ill (adv.) on model of wealth (also see -th (2)).

[S]uch things, and so much of them as he can use, are, indeed, well for him, or Wealth; and more of them, or any other things, are ill for him, or Illth. [Ruskin, "Munera Pulveris"]

"the character of being ill-disposed toward another or others; ill-will, malice, personal hatred," mid-15c., from Old French malevolence and directly from Latin malevolentia "ill-will, dislike, hatred," from malevolentem (nominative malevolens) "ill-disposed, wishing ill, spiteful, envious," from male "badly" (see mal-) + volentem (nominative volens), present participle of velle "to wish" (see will (v.)) 

"suit ill, be unfitting," 1520s, from mis- (1) "badly, wrongly" + become.

mid-13c., "harboring ill-will, enmity, or hostility," from Old French malicios "showing ill will, spiteful, wicked" (Modern French malicieux), from Latin malitiosus "wicked, malicious," from malitia "badness, ill will, spite," from malus "bad, unpleasant" (see mal-). In legal use (early 14c., Anglo-French), it means "characterized by malice prepense" (see malice).