monotone
nounUK /ˈmɒnətəʊn/
US /ˈmɑːnətoʊn/
A voice that stays on the same level and does not go up and down.
The teacher spoke in a monotone, so the class felt sleepy.
OTHER MEANINGS
2. A sound or piece of music that stays on one note without changing.
The singer held a single monotone for a long time.
3. Having only one color or shade, with no variety.
The painting was a monotone of gray and white.
4. Boring because it never changes.
His monotone routine made the show feel long.