Definition of permanent hardness in English:

permanent hardness

Line breaks: per¦man|ent hard|ness

Entry from British & World English dictionary

noun

[mass noun]
The presence in water of mineral salts (chiefly calcium sulphate) that are not removed by boiling.

Definition of permanent hardness in:

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Word of the day envenom
Pronunciation: enˈvenəm
verb
put poison on or into; make poisonous