'cachectic' originates from New Latin 'cachexia', ultimately from Greek 'καχεξία' (kakhexia), where the prefix 'kak-' (κακ-) meant 'bad' and 'hexis' (ἕξις) meant 'condition'.

'cachectic' developed as an adjective from the noun 'cachexia' (New Latin), which itself came from Greek 'καχεξία'; the medical noun entered English in the 18th–19th century and the adjective 'cachectic' was formed subsequently to describe the wasting condition.

Initially it referred broadly to a 'bad condition' (in Greek), but over time it narrowed in medical usage to mean the specific wasting syndrome 'cachexia' and, as an adjective, 'relating to or showing severe wasting'.