Both Uses

rein
in
Jane Eyre
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Some years older than I, she knew more of the world, and could tell me many things I liked to hear: with her my curiosity found gratification: to my faults also she gave ample indulgence, never imposing curb or rein on anything I said.†
p. 93.1 *
The forehead declares, 'Reason sits firm and holds the reins, and she will not let the feelings burst away and hurry her to wild chasms.†
p. 233.3

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)