All 7 Uses

rein
in
The Horse and His Boy
(Edited)

When all was finished it said: "Now; we've got to have reins for the look of the thing, but you won't be using them."
Chpt 1

reins = a means of control -- most commonly the straps attached to a bit in a horse's mouth that are used to control it OR restrains or controls
If I'm not to hold on by the reins or by your mane, what am I to hold on by?
Chpt 1 *

reins = straps used to control a horse
But in spite of semi-darkness and cold fingers all was done in the end, the big packs bound on the horses, the rope halters (which they were now wearing instead of bridles and reins) in the children's hands, and the journey began.
Chpt 3

reins = a means of control -- most commonly the straps attached to a bit in a horse's mouth that are used to control it OR restrains or controls
Shasta's seat was excellent but he was sadly puzzled what to do with his reins, for he had never touched the reins while he was on Bree's back.
Chpt 11
Shasta's seat was excellent but he was sadly puzzled what to do with his reins, for he had never touched the reins while he was on Bree's back.
Chpt 11
Shasta told Corin most of his adventures and explained that he had learned all his riding from a horse and didn't really know how to use the reins.
Chpt 13
And he'd got the reins tangled somehow.
Chpt 13

Definitions:

(1) (rein as in: to rein in their activities)
to restrain or control; or a means of control
The meaning of rein depends upon its context. For example:
- "keep a tight rein on the new employee," or "rein in a horse" -- to control or restrain
- "give the new employee free rein," or "give the horse full rein" -- do not restrain
- "the reins of government" -- means of control
- "the reins of the horse" -- leather straps used with a bit to control a horse (You might like to think of other senses of rein as being figurative derivations from this sense.)
(2) (meaning too rare to warrant focus)
to "give free rein" is not to restrain (not to exercise control over)