Reins (r?nz), n. pl. [F. rein, pl. reins, fr. L. ren, pl. renes.]
The kidneys; also, the region of the kidneys; the loins.
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.
Prov. xxiii. 16.
I am he which searcheth the reins and hearts.
Rev. ii. 23.
Reins of a vault Arch., the parts between the crown andd 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.
© Webster 1913.