Webster's Revised Unabridged Dictionary · 1913

Reins

Reins (rānz) , noun, plural

[French rein, pl. reins, from Latin ren, pl. renes.]

1.
The kidneys; also, the region of the kidneys; the loins.
2.
The inward impulses; the affections and passions; -- so called because formerly supposed to have their seat in the part of the body where the kidneys are.
My reins rejoice, when thy lips speak right things. — Bible (KJV) - Proverb xxiii. 16
I am he which searcheth the reins and hearts. — Rev. ii. 23
Collocations (1)
Reins of a vault (Architecture) , the parts between the crown and the spring or abutment, including, and having especial reference to, the loading or filling behind the shell of the vault. The reins are to a vault nearly what the haunches are to an arch, and when a vault gives way by thrusting outward, it is because its reins are not sufficiently filled up.