a kidney (as a general emotional center), the reins.
Strong's:
νεφρός
a kidney (plural), i.e. (figuratively) the inmost mind Derivation: of uncertain affinity;
KJV Usage: reins.
TBESG:
νεφρός
mind
G:N-M
νεφρός, -οῦ, ὁ [in LXX for כִּלְיָה, Exo.29:13, al.; metaph., Refs Psa.7:9 16:7 26:2, Wis.1:6, al. ;] a kidney; pl., the kidneys, reins; metaph., of the will and affections: ν. καί καρδίαι (thoughts), Rev.2:23.† (AS)
Thayer:
1) a kidney 2) kidneys, loins 2a) used of the inmost thoughts, feelings, purposes, of the soul
νεφρός
nephros
nef-ros'
Of uncertain affinity; a kidney (plural), that is, (figuratively) the inmost mind