(metallurgy) Metal that is harder at its surface, due to a case hardening process.

Alternative spelling of case hardened / Hardened by experience.

An English and Irish surname transferred from the given name.

(nautical) A large, hard biscuit made from unleavened flour and water; formerly used as a long-term staple food aboard ships.

(botany) Of a plant: requiring protection against frost.

(botany) A plant that requires protection against frost.

A perennial flowering plant, Campanula rotundifolia, native to the Northern Hemisphere, with blue, bell-like flowers.

(nonstandard, or attributive) Alternative spelling of hard hat / (slang) A person who wears a hard hat, such as a construction worker.

A helmet, usually made from rigid plastic, used on construction sites to protect the head from falling objects.

A person who takes a firm, uncompromising position on some policy.