The Spanish word 'bellaco' (meaning 'rogue' or 'villain') comes from the Latin word 'bellum' meaning 'war', combined with the Spanish pejorative suffix '-aco'. The pejorative suffix '-aco' adds a negative or derogatory connotation to the base word. So a 'bellaco' literally developed from the concept of someone associated with war, but in a negative way, eventually coming to refer to a person of bad character - a rogue or villain.

Some related Spanish words that share the Latin root 'bellum' include 'bélico' (warlike), 'belicoso' (bellicose, warlike), and 'bélica' (relating to war). While these words maintained their direct connection to the concept of war, 'bellaco' evolved to describe the negative character traits that might be associated with warfare or conflict.

English speakers might recognize the Latin root 'bellum' in words like 'belligerent' (hostile and aggressive), 'bellicose' (demonstrating aggression and willingness to fight), and 'antebellum' (before the war). While these English words maintained their connection to the concept of war and conflict, the Spanish 'bellaco' took on a broader meaning of general villainy or roguish behavior.