The quality or condition of having an ectomorphic body type, or the state of being naturally thin and lean.
From 'ectomorph' + '-ism' (a doctrine or condition). Created in the 1940s as part of Sheldon's systematic classification of human body types.
This word is rarely used because 'ectomorph' or 'ectomorphic' do the job better—it's an example of how not every '-ism' word survives in English!
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