Definitions
1.verbTo become hard (tough, resistant to pressure).
2.verbTo make something hard or harder (tough, resistant to pressure).
3.verbTo strengthen.
4.verbTo modify (a website or other system) to make it resistant to malicious attacks.
5.verbTo become or make (a person or thing) resistant or less sensitive.
6.verbTo become or make (a consonant) more fortis.
7.adjectiveUnfeeling or lacking emotion due to experience; callous."The bloody scene could reduce even the most hardened soldier to tears."
8.adjectiveFirmly established or unlikely to change; inveterate.
9.adjectiveHaving extra defences against attack; highly fortified."a hardened air base"