Emily Dickinson Lexicon

supremacy, n. [see supreme, adj.]

1. Greatness; prominence; significance.
2. God; a ruling and reigning being above and beyond death; existence beyond mortality; (compare this use of “Supremacy” with “Supreme” in Poem 455: “When Truth … Advance unmoved – to Her Supreme – / Her God – Her only Throng”. In Webster's 1844 entry for “supremacy,” he makes reference to the “supremacy of the king [of England] in spiritual affairs” both in his example for definition 1 and in the definition of the phrase “Oath of Supremacy.” Could ED be making a connection with this earthly king's “supremacy” over the pope, and God, the heavenly king's supremacy over death and mortality? Poem 1565 was written, apparently, after Gilbert's death, so I think this might be the connection she was pointing to).