harden
verb
hard·en
| \ ˈhär-dᵊn
\
\
hardened;
hardening\ ˈhärd-niŋ
, ˈhär-dᵊn-iŋ \
, ˈhär-dᵊn-iŋ \
Definition of harden
(Entry 1 of 3)
1
: to make hard or harder
2
: to confirm in disposition, feelings, or action
especially
: to make callous
hardened his heart
b
: to inure to unfavorable environmental conditions (such as cold)
—often used with off harden off seedlings before transplanting
4
: to protect from blast, heat, or radiation (as by a thick barrier or placement underground)
1
: to become hard or harder
2a
: to become firm, stable, or settled
b
: to assume an appearance of harshness or severity
her face hardened at the thought
3
: to become gradually acclimatized to unfavorable conditions
—often used with off plants hardened off before the first frost