mesoderm n.

before vowels mes-, word-forming element meaning "middle, intermediate, halfway," from Greek mesos "middle, in the middle; middling, moderate; between" (from PIE root *medhyo- "middle").

word-forming element meaning "skin," from Greek derma "skin, hide, leather," from PIE root *der- "to split, flay, peel," with derivatives referring to skin and leather.

"person with a powerful, compact body build," 1940, from mesoderm + -morph, from Greek morphe "form, shape; beauty, outward appearance," a word of uncertain etymology. Coined by American psychologist William H. Sheldon (1898-1977); the reference is to the mesodermal layer of the embryo, from which physical structures develop. Related: Mesomorphic (attested from 1923 in chemistry, a separate coinage in reference to a state of a liquid crystal).