The spelling of the word "externa" can be confusing. The correct pronunciation is /ɪkˈstɜːnə/, with emphasis on the second syllable. The reason for the spelling is due to its Latin origin, where the letter "x" represented the "ks" sound. This sound was later simplified to just "s" in English, but the spelling of the word remained the same. "Externa" means "external" and is often used in medical terminology to refer to external structures of the body.
The word "externa" is derived from the Latin word "externus", which means "external" or "foreign". It comes from the combination of the prefix "ex-" meaning "out" and the root "ternus" meaning "three". The original meaning of "externus" in Latin referred to things that were on the outside or beyond a specific boundary. Over time, it has been adopted into various languages and contexts with slightly different meanings, but the etymology remains rooted in its Latin origins.