The Spanish word 'complexión' (meaning 'constitution' or 'temperament') comes from the Latin word 'complexio', which meant 'combination' or 'nature'. The Latin term was formed from two parts: the prefix 'com-' meaning 'together' and the verb 'plectere' meaning 'to weave or braid'. So literally, the original concept was about things being 'woven together', which evolved to describe a person's overall physical and mental makeup or constitution.

This word is related to other Spanish words like 'complejo' (complex) and 'complicado' (complicated), which share the same Latin roots of weaving or braiding things together. While 'complexión' specifically refers to one's physical constitution, these related words maintain the sense of things being interwoven or combined in some way.

English speakers might recognize the connection to words like 'complex', 'complexion', and 'complexity'. While the English word 'complexion' now primarily refers to the appearance or color of the skin, it originally had the same meaning as Spanish 'complexión', referring to one's general physical constitution. All these words preserve the original notion of different elements being woven or combined together.