hardness (n.)
- abstruseness
- arduousness
- armor
- asperity
- astringency
- austerity
- burdensomeness
- callosity
- callousness
- callus
- closeness
- cohesiveness
- coldheartedness
- coldness
- compactness
- complexity
- complication
- congestion
- consistence
- consistency
- crabbedness
- cruelty
- deepness
- denseness
- density
- difficultness
- difficulty
- durability
- esoterica
- firmness
- fundamentalism
- gluiness
- grimness
- hairiness
- hardheartedness
- hardiness
- hardship
- harshness
- heartlessness
- impenetrability
- impenitence
- impermeability
- imperviousness
- inclemency
- incompressibility
- induration
- inexorability
- inexorableness
- inflexibility
- insensitiveness
- insensitivity
- insolence
- intricacy
- knottiness
- laboriousness
- lastingness
- mercilessness
- obduracy
- obstinacy
- onerousness
- oppressiveness
- orthodoxy
- pitilessness
- profoundness
- profundity
- purism
- puritanism
- reconditeness
- relentlessness
- resistance
- rigidity
- rigidness
- rigor
- rigorousness
- ropiness
- roughness
- ruggedness
- ruthlessness
- severity
- solidity
- solidness
- soundness
- stability
- stamina
- staunchness
- sternness
- stiffness
- stoutness
- strength
- strenuousness
- stringency
- stubbornness
- sturdiness
- temper
- tenacity
- thickness
- toilsomeness
- toughness
- troublesomeness
- unbreakableness
- unfeelingness
- unmercifulness
- unnaturalness
- unresponsiveness
- unyieldingness
- vicissitude
- vigor
- viscidity
- viscosity
- viscousness
- vitality
