harden

Etymology 1

From Middle English hardenen, equivalent to hard + -en. Cognate with Danish hærdne (“to harden; cure”), Swedish hårdna (“to harden”), Norwegian herdne (“to harden”), Icelandic harðna (“to harden”).

verb

1. (intransitive) To become hard (tough, resistant to pressure).
2. (transitive, ergative) To make something hard or harder (tough, resistant to pressure).
3. (transitive, figurative) To strengthen.
   In view of the system's relatively low cost, the preferred alternative could be for the military user to avail himself of multiple base stations rather than seeking to harden the base station hardware for defense applications. 2002, Jane's International Defense Review, volume 35
   Ramos had locked Salah’s right arm and turned him, judo-style, as they lost balance going for the same ball. Television replays hardened the suspicion it was a calculated move on Ramos’s part and, when Salah landed with a hell of a thud, the damage was considerable. 26 May 2018, Daniel Taylor, “Liverpool go through after Mohamed Salah stops Manchester City fightback”, in The Guardian (London)
4. (transitive, computing) To modify (a website or other system) to make it resistant to malicious attacks.
5. (transitive, intransitive) To become or make (a person or thing) resistant or less sensitive.
   When thou goest to return into Egypt, see that thou do all those wonders before Pharaoh, which I have put in thine hand: but I will harden his heart, that he shall not let the people go. KJV, Exodus 4:21
6. (intransitive, informal) To get an erection.
   He hardened as he imagined himself running his hands over her small breasts 2 Aug 1999, Karen Mitchell, “Files from the Feminet BBS NOVAD5.TXT 38.38 KB”, in alt.sex.stories.tg (Usenet)
7. (transitive, intransitive, phonology) To become or make (a consonant) more fortis; to (cause to) undergo fortition.
8. (Slavic phonology) To unpalatalize or velarize.
   Of course one needs to keep in mind the fact that *tʹ and *dʹ are hardened before *e and *i in Ukrainian and Rusyn[…] 2007, Stefan Pugh, A New Historical Grammar of the East Slavic Languages
   Belarussian preserved soft labials before vowels, hardened rʹ to r, and affricated tʹ and dʹ[…] 2013-02-01, Philipp Strazny, Encyclopedia of Linguistics, Routledge, page 914

Etymology 2

noun

1. Alternative form of hurden (“coarse linen”)