The Spanish word 'sicario' meaning 'hired assassin' comes from the Latin word 'sicarius', which meant 'assassin' or 'murderer'. The Latin term 'sicarius' itself is formed from two parts: the noun 'sica' meaning 'dagger' and the suffix '-arius' meaning 'belonging to' or 'associated with'. So literally, a 'sicarius' was someone associated with or who used a dagger - essentially a knife-wielding killer. This term evolved directly into the Spanish 'sicario', maintaining its meaning of a professional killer or hitman.

While 'sicario' is a relatively specific term in Spanish, it doesn't have many common related words in modern Spanish. This is because the Latin root 'sica' (dagger) didn't produce many other derivatives in Spanish.

While English doesn't have any common modern words directly related to 'sicario', the term 'sicarian' exists as a rare word meaning 'assassin' or 'murderer', also derived from the Latin 'sicarius'. The word appears occasionally in historical or academic contexts when discussing ancient Roman assassins.