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.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI