In the medieval world that Middle-earth parallels, everyone had a Master, to
whom they owed allegiance and service, rising in a continual relationship right
up to the King and/or Pope -- and they acknowledged God as their master.
Tolkien, by saying Tom is his own Master, is using this specific meaning. It
emphasizes how much of an anomaly he is.
He does not "own" his land or its inhabitants, but he does have power, for he
is Master of his own land, and every thing in it gives him service as needed.
The power Tom has "rejected" is any power outside his own land, and that power
includes everything up to and including the affairs of the Valar themselves.
But he is very much an anomaly in Tolkien's universe, and cannot really be
discussed in the same breath with any other aspect of
LotR.

"Wake up and smell the coffee."
squire online:
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