monotony

Noun

• constancy of tone or pitch or inflection

• the quality of wearisome constancy, routine, and lack of variety
  • he had never grown accustomed to the monotony of his work
    
  • he was sick of the humdrum of his fellow prisoners
    
  • he hated the sameness of the food the college served
    

Related words

• Synonyms: 
  humdrum , sameness