Noah Webster
Toughness
TOUGHNESS, noun tuf'ness. The quality of a substance which renders it in some degree flexible, without brittleness or liability to fracture; flexibility with a firm adhesion of parts; as the toughness of steel.
1. Viscosity; tenacity; clamminess; glutinousness; as the toughness of mucus.
2. Firmness; strength of constitution or texture.