A rigorous examiner of another's feelings or conscience (chiefly as a title of God or Christ). In later use also: a person who rigorously examines his or her own feelings or conscience.
Origin
Early 17th century. From heart + searcher.
Definition of heart-searcher in US English:
heart-searcher
nounˈhɑːtˌsəːtʃə
rare
A rigorous examiner of another's feelings or conscience (chiefly as a title of God or Christ). In later use also: a person who rigorously examines his or her own feelings or conscience.