The Spanish word 'cuartillo' comes from combining the Spanish word 'cuarto' (meaning 'fourth') with the diminutive suffix '-illo'. The word 'cuarto' itself derives from Latin 'quartus' meaning 'fourth'. The addition of the diminutive suffix '-illo' gives the meaning of 'small fourth part'.

This formation pattern is typical in Spanish, where diminutive suffixes like '-illo' are added to existing words to indicate something smaller or lesser in size or importance.

Several common Spanish words are related to 'cuartillo' through their shared root with 'cuarto': 'cuarto' (fourth, quarter, room), 'cuarta' (quarter, fourth part), and 'cuartel' (quarters, barracks). All these words carry the basic meaning of 'fourth' or 'quarter' in different contexts.

English speakers can relate 'cuartillo' to several familiar English words that come from the same Latin root 'quartus': 'quarter', 'quart', 'quartet', and 'quarters'. All these words maintain a connection to the concept of 'four' or 'fourth part'. For example, a 'quarter' is a fourth part, a 'quart' is a fourth of a gallon, and a 'quartet' is a group of four.