ectomorph

n.
An individual having a lean, slightly muscular body build in which tissues derived from the embryonic ectoderm predominate.

[ECTO(DERM) + -MORPH.]

Description given to a tall, thin person, possibly with underdeveloped muscles. See also endomorph; mesomorph.

(ek′tōmôrf)
n

A constitutional body type (Sheldon’s classification) characterized by long, fragile bones and a highly developed nervous system.

A dimension of somatotype (body build) characterized by a tall, thin, and linearly constructed body. See also somatotype.