ECTOMORPH

ectomorph

(noun) a person with a thin body

Source: WordNet® 3.1

Etymology

Noun

ectomorph (plural ectomorphs)

Someone with a lean, only slightly muscular body

(bodybuilding): 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.

Synonyms

• hard gainer

Source: Wiktionary