fiz. hardness
~ metali - metal hardness
~ wody - hydr. water hardness
1. (the property of being rigid and resistant to pressure
not easily scratched
measured on Mohs scale) 
hardness 
synonim: nieelastyczność
2. (the trait of being resolute
 "his resoluteness carried him through the battle"
 "it was his unshakeable resolution to finish the work") 
resoluteness, firmness, firmness of purpose, resolve, resolution: : synonim: niewzruszoność
(materiału) hardness
(spoistość, zwięzłość) firmness
(nieustępliwość) toughness
 ~ wody water hardness
 próba ~ści hardness test
 n fem U hardness
(fig) firmness
strictness.twardy adj 
1. (sztywny) hard
 tough
 stiff
 (anat): ~e podniebienie hard palate
 ~a woda hard water
 (idm): ~ orzech do zgryzieniaa hard nut to crack
 ~ jak skała hard as a rock. 
2. (fig, nieugięty,  bezwzględny) rigid
 strict
 firm: ~e zasady rigid rules
 ~a dyscyplina rigour
 ~a konieczność dire necessity. 
3. (nieczuły) hard
 cold
 insensitive:  o ~m sercu hardhearted
 coldhearted
 insensitive. 
4. (fig,  o człowieku - zahartowany) tough: ~ facet tough guy
 (fig, stabilny) firm
 stable
 steadfast: ~a szkoła hard school
 ~a ręka heavy/iron hand
hardness n
HARDNESS
TOUGHNESS
SEVERITY
INFLEXIBILITY
RIGOUR
RIGOR
STIFFNESS
hardness
~ ogólna wody - total water hardness
~ węglanowa (przemijająca) wody carbonate hardness, alkaline hardness
~ wody water hardness
f hardness testing machine, hardness tester, sclerometer
endurance
firmness
rigidity