Rabbi Julian Sinclairs dip into the dictionary
Reshut is a word imbued with multiple religious and colloquial meanings. Originally it meant power, authority or control. Belief in the existence of two reshuyot, ultimate powers, one controlling good and the other evil, was the classic dualist heresy (see Talmud Hagigah 15a).
In rabbinic writings, the Reshut generally means the Roman government. Pirkei Avot (Ethics of the Fathers) cautions Dont become too familiar with the Reshut (1:10). Rashi explains that governments never befriend anyone except for their own ends.
Talmud Avodah Zarah (17a) carries this suspicion still further and warns that the voices of two insatiable powers emanate from hell; one is the voice of reshut. This ancient wariness of authority arguably colours Jewish politics to this day.
In legal literature, a reshut means domain. The basic Torah prohibitions on Shabbat carrying are to transport an object from a reshut hayachid (private domain) to a reshut harabim (public domain) and vice versa, and also to carry something six feet or more in a reshut harabim.
Reshut also means permission. When we say grace after meals in a group of people, the leader declares breshut rabbotai, etc. thereby asking leave of the others present to begin.
These meanings have a number of present-day continuations, particularly in more yeshivish communities. It can mean permission, as in No one in the yeshivah has reshus to wear tefillin the whole day: or territory/ private property, as in At least in the reshus of my own room I can enjoy the music I like.