sameness

noun

1. The quality of being the same; identity.

   “All of them agreed that the working-classes must be kept in their place; and all of them perceived that American Democracy did not imply any equality of wealth, but did demand a wholesome sameness of thought, dress, painting, morals, and vocabulary.”

   “However strange it may sound, it always seemed to me […] that Adrian's laughter-filled friendship with Schildknapp had something to do with the sameness of their eye color”

2. The state of being equivalent; equality.
3. A tiring lack of variety; monotony.

   “[…] in the time when day follows day in dull, unexpectant sameness, and trial is a dreary routine,—it is then that despair threatens […]”

   “O to sail to sea in a ship! / To leave this steady unendurable land, / To leave the tiresome sameness of the streets, the sidewalks and the houses, / To leave you O you solid motionless land, and entering a ship, / To sail and sail and sail!”