The Spanish word 'grueso' meaning 'thick' comes directly from the Latin word 'grossus', which meant 'thick' or 'large'. The evolution from Latin to Spanish shows a typical sound change where the Latin '-ss-' became '-s-' in Spanish, and the Latin 'o' developed into the Spanish diphthong 'ue', a common phonetic development in Spanish words.

A related Spanish word is 'grosero' meaning 'rude' or 'coarse', which also comes from Latin 'grossus'. The semantic connection is that something 'coarse' or 'unrefined' was considered 'thick' or 'rough' in texture. Similarly, 'grosor' meaning 'thickness' is another commonly used related word.

English speakers might recognize the connection to words like 'gross', which also comes from Latin 'grossus'. While 'gross' in modern English has taken on meanings like 'disgusting' or 'total' (as in 'gross income'), its original meaning of 'thick, coarse, or large' is closer to the Spanish 'grueso'. This can still be seen in terms like 'gross weight' (total weight) or 'gross misconduct' (serious misconduct).