Assassino vs. omicida
The Italian words assassino and omicida both refer to someone who kills, but they have distinct connotations and usage in the Italian language.
Assassino
B1Assassino typically refers to a person who commits murder in a premeditated or treacherous manner, often for hire or personal gain.
L'assassino del politico non è stato ancora catturato.
(The assassin of the politician has not been caught yet.)
Il film racconta la storia di un assassino professionista.
(The movie tells the story of a professional hitman.)
Omicida
B2Omicida is a more general term for a person who kills another human being, regardless of the circumstances or motivation.
L'omicida ha confessato il crimine alla polizia.
(The killer confessed the crime to the police.)
Il conducente ubriaco è stato accusato di omicidio colposo.
(The drunk driver was charged with manslaughter (literally: culpable homicide).)
Summary
While both assassino and omicida refer to killers, assassino implies a more specific type of murderer, often associated with planned or professional killing. Omicida is a broader term that can apply to any person who has taken a life, intentionally or not. Assassino is more commonly used in dramatic or sensational contexts, while omicida is more neutral and often used in legal or formal situations.