The Collaborative International Dictionary of English v.0.48:
Reins \Reins\ (r[=a]nz), n. pl. [F. rein, pl. reins, fr. L. ren,
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.
I am he which searcheth the reins and hearts. --Rev.
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.
Moby Thesaurus II by Grady Ward, 1.0:
83 Moby Thesaurus words for "reins":
Oregon boat, back band, backstrap, bearing rein, bellyband, bilbo,
bit, blinders, blinds, bond, bonds, breeching, bridle, camisole,
caparison, cavesson, chains, checkrein, cheekpiece, chinband,
cinch, collar, crownband, crupper, cuffs, curb, fetter, gag,
gag swivel, girth, gyves, hackamore, halter, hames, hametugs,
hamper, handcuffs, harness, headgear, headstall, helm, hip straps,
hobbles, hopples, irons, jaquima, jerk line, leading strings,
leash, lines, manacle, martingale, muzzle, noseband, pillory,
pole strap, reins of government, restraint, restraints, ribbons,
rudder, saddle, shackle, shaft tug, side check, snaffle, stocks,
straightjacket, strait-waistcoat, straitjacket, stranglehold,
surcingle, tack, tackle, tether, tiller, trammel, trammels,
trappings, tug, wheel, winker braces, yoke
Easton's 1897 Bible Dictionary:
the kidneys, the supposed seat of the desires and affections;
used metaphorically for "heart." The "reins" and the "heart" are
often mentioned together, as denoting the whole moral
constitution of man (Ps. 7:9; 16:7; 26:2; 139:13; Jer. 17:10,