A hardening of the heart; hardness of heart.(noun)
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Use "obduration" in a sentence
"Scripture denotes rather obduration against God than against men."
"That there is a judicial obduration upon the people whom they are determined against, accompanying them; that no calls to repentance or reformation shall be complied withal so as to divert them."
"By this means is the heart prepared for a farther obduration in sin, by the confirmation of native obstinacy."