The Spanish word 'anoréxico' (meaning 'anorexic') comes from combining the Spanish noun 'anorexia' with the adjective suffix '-ico'. The word 'anorexia' itself has ancient Greek origins, formed from two parts: the prefix 'an-' meaning 'without' and 'órexis' (ὄρεξις) meaning 'appetite'. These combined to form 'anorexía' (ἀνορεξία) in Greek, literally meaning 'lack of appetite'. This term was borrowed into Latin as 'anorexia' and eventually made its way into Spanish with the same spelling.

Some related Spanish words include 'anorexia' (the noun form) and other adjectives ending in '-ico' like 'alérgico' (allergic) or 'artístico' (artistic). The suffix '-ico' is commonly used in Spanish to form adjectives from nouns, especially in medical and scientific terms.

English speakers will recognize the cognate word 'anorexic' and 'anorexia', which share the exact same Greek origins. The English language also uses many medical and psychological terms with the Greek prefix 'an-' meaning 'without' or 'lacking', such as 'anemia' (without blood), 'anaesthetic' (without feeling), and 'anonymous' (without name).