sameness

noun3

1. •
   The quality of being the same; identity.

   • 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 — 1997
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 […] — 1860