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Webster 1913 Edition

(sĭn′ȧr-ky̆)

Noun.

[Gr.

συναρχία

, fr.

συνάρχειν

to rule jointly with;

σύν

with +

ἄρχειν

to rule.]

Joint rule or sovereignty.

[R.]

Stackhouse.

Noun.

[Gr.] Joint rule or sovereignty.

synarchy ‎(plural synarchies)

Joint rule or sovereignty.
- 1767, Thomas Stackhouse, A new history of the Holy Bible (book VI)
  The synarchies, or joint reigns of father and son, in these times, have rendered the chronology a little difficult […]