The Spanish word 'partisano' (meaning 'partisan') comes from Italian 'partigiano', which was formed from two Latin elements: 'pars' meaning 'part' and the suffix '-ensianus' meaning 'belonging to'. The word literally developed from the concept of someone belonging to a particular part or faction.

This word is related to the common Spanish word 'parte' (part), which comes from the same Latin root 'pars'. You can think of a 'partisano' as someone who takes a 'parte' (part) or side in a conflict or cause.

The English word 'partisan' is directly related to 'partisano', both coming from the same Italian source 'partigiano'. English also has many related words from the Latin 'pars' root, such as 'part', 'partial', 'participate', and 'partition'. Just as a 'partisan' takes a particular part or side, these words all relate to the concept of parts or division.