The Spanish word 'basílica' comes from the Latin word 'basilica', which meant a public building or hall. This Latin term was borrowed from Ancient Greek 'basilike' (βασιλική), meaning 'royal' or 'regal', which itself derived from 'basileus' (βασιλεύς), meaning 'king'. Originally, a basilica was a type of public building in ancient Rome used for business and legal matters. Over time, as Christianity spread throughout the Roman Empire, many of these buildings were converted into churches, and the term came to specifically refer to an important or significant church building, particularly those granted special ceremonial rights by the Pope.

While 'basílica' itself is a relatively specific architectural and religious term, Spanish has some related words that share the same Greek root referring to royalty. For example, 'basilisco' (basilisk) comes from the same Greek root and literally means 'little king', as this mythical creature was considered the king of serpents.

English speakers might recognize this word in the identical English word 'basilica', which has the same meaning and etymology. The same Greek root gives us other English words like 'basilisk' (the mythical king of serpents) and 'basil' (the herb, named because it was considered the 'king of herbs'). The word 'basel' in some names (like Basel, Switzerland) also comes from this same Greek root meaning 'royal'.