ectomorph

Noun

1. Someone with a lean, only slightly muscular body
   • Also there was a woman I hadn't met, a chain-smoking French ectomorph whose job it was to make sense of records of public spending in the Ministry of Finance. - 1990, Robert Klitgaard, Tropical Gangsters: One Man's...
2. : Theoretical body type in which a person has a high metabolism. Such a person can easily maintain a low fat physique, but does not add muscle or body weight easily.
   • The ectomorph body type is characterized by narrow shoulders and hips and a lean build. Its naturally fast metabolism makes it easy for ectomorphs to lose or maintain body fat levels but more difficult to build muscle....