The Spanish word 'anoréxica' (meaning 'anorexic' in its feminine form) comes from the Spanish noun 'anorexia' combined with the feminine adjectival suffix '-ica'. The word 'anorexia' itself has ancient Greek origins, being derived from 'ἀνορεξία' (anorexia), which was formed by combining two Greek elements: the prefix 'an-' meaning 'without' and 'ὄρεξις' (orexis) meaning 'appetite' or 'desire'. This compound literally meant 'lack of appetite' in Greek. The word entered Spanish through Latin 'anorexia', maintaining the same meaning.

A related Spanish word is 'anorexia' itself, which is more commonly used as a noun to refer to the eating disorder. While 'anoréxica' is specifically the feminine adjective form used to describe someone who has anorexia or something related to anorexia, 'anorexia' is the condition itself.

The English words 'anorexia' and 'anorexic' are direct cognates of the Spanish words, sharing the exact same Greek origins. The English terms were also borrowed through medical Latin, which is why they look and sound so similar to their Spanish counterparts. The main difference is just in the spelling and pronunciation of the adjectival form: English uses '-ic' where Spanish uses '-ica' for the feminine form.