Wiktionary
                    ectomorphic
                    
                        
                
                                                                    a. of or pertaining to an ectomorph
WordNet
                    ectomorphic
                    
                        
                
                                                                    adj. having a lightly-muscled build with long limbs [ant: endomorphic, mesomorphic]
Usage examples of "ectomorphic".
Tee loved his food as much as she did, though his frame was the ectomorphic sort that would never wear excess weight for long.
He was more communicative than Poulsen, whom he vaguely resembled, being ectomorphic and seemingly of no particular age.