/sin'deuh ree"sis/ , n.
1. innate knowledge of the basic principles of morality.
2. Christian Mysticism. the essence of the soul that unites with God.
Also, synteresis .
[ 1350-1400; ME synderesis, synteresis syntéresis a guarding, equiv. to syntere-, var. s. of syntereîn to guard closely ( syn- SYN- + tereîn to guard) + -sis -SIS ]