ec·to·mor·phic
Pronunciation: \ˌek-tə-ˈmȯr-fik\
Function: adjective
Etymology: ectoderm + -morphic; from the predominance in such types of structures developed from the ectoderm
Date: 1940
1 : of or relating to the component in West H. Sheldon's classification of body types that measures the body's degree of slenderness, angularity, and fragility
2 : characterized by a lean slender body build with slight muscular development

(from Sunday Times' Hot Bods)