monotonous

adj

1. Having an unvarying pitch or tone.

   “"But my daughter—but the Lady Eveline"—said the Fleming, with some slight change in his monotonous voice, which seemed to express doubt and perplexity—"You are cruel conquerors, and—"”

2. Tedious, repetitious, or lacking in variety.

   “[L]istening for a moment, she heard the monotonous and heavy tread of the soldier echoing through the passage.”