Both Uses

rein
in
Sycamore Row
(Auto-generated)

If the case settled now, his fees would be severely reined in.†
p. 307.5 *

reined in = restrained
Seth had the reins, I was holding on for dear life, but we rode bareback all the time and we knew what we were doing.†
p. 607.3

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)