- monotone, monotonic, monotonous - sounded or spoken in a tone unvarying in pitch; "the owl's faint monotonous hooting"
Antonyms: melodious, melodic, musical (indirect, via unmelodious)
- humdrum, monotonous - tediously repetitious or lacking in variety; "a humdrum existence; all work and no play"; "nothing is so monotonous as the sea"
Antonym: lively (indirect, via dull)