The Spanish vulgar slang term 'gilipollas' (meaning 'dickhead' or 'fool') is a compound word that combines two elements: 'gil' and 'polla'. The first element 'gil' comes from the Caló (Spanish Romani) word 'jili' meaning 'foolish' or 'naive'. Caló was the language of Spanish Romani people that influenced Spanish slang significantly. The second element 'polla' is a vulgar Spanish word for 'penis'. The combination creates a colorful insult that literally combines the concepts of foolishness and a crude anatomical reference.

A simpler and less vulgar related Spanish word is 'gil', which means 'fool' or 'simpleton'. This word is still used in modern Spanish as a milder insult. You might hear phrases like 'ser un gil' (to be a fool) or 'no seas gil' (don't be foolish).

While there aren't any direct English cognates for 'gilipollas' since it comes from Caló and Spanish sources, it's worth noting that the construction of this compound insult (combining words for 'fool' and a vulgar anatomical term) is similar to how English creates insults like 'dickhead' - though these arose independently.