Reins \Reins\ (r[=a]nz), n. pl. [F. rein, pl. reins, fr. L. ren, pl. renes.] 1. The kidneys; also, the region of the kidneys; the loins. [1913 Webster] 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. [1913 Webster] My reins rejoice, when thy lips speak right things. --Prov. xxiii. 16. [1913 Webster] I am he which searcheth the reins and hearts. --Rev. ii. 23. [1913 Webster] {Reins of a vault} (Arch.), 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. [1913 Webster]