Monotonous (adjective)

1. Lacking in variety; tedious and unvarying.
2. Having an unchanging tone or pitch, as a sound.

Origin:

From the greek word "monos" meaning "single" and "tonos" meaning "tone".

Examples:

1. The monotonous sound of the raindrops was lulling me to sleep.
2. The job was monotonous and required little mental effort.
3. The lecture was monotonous and I found myself struggling to stay awake.
4. The monotonous landscape was uninspiring and dull.
5. The monotonous life in the small town was driving her crazy.