(a.) Not ductile; incapable of being drawn into threads, as a metal; inelastic; tough.

adamant adamantine immovable immutable inelastic inextensible inextensile inextensional inflexible intractable intractile irresilient nonelastic nonstretchable stubborn unalterable unbending unextendible unextensible unflexible ungiving unlimber unmalleable unpliable unpliant untractable unyielding