set like concrete (8)
(Other definitions for hardened that I've seen before include "Inured" , "describing some criminals" , "Tough, cynical" , "Became obdurate" , "Toughened" .)
(Other definitions for harden that I've seen before include "Become stronger or firmer" , "Set; become tougher" , "Become less soft" , "Temper, steel say" , "Become firm or tough" .)