1. (noun)monotone, drone, droning an unchanging intonation
2. (adj)monotone a single tone repeated with different words or different rhythms (especially in rendering liturgical texts)
3. (adj)monotonic, monotone of a sequence or function; consistently increasing and never decreasing or consistently decreasing and never increasing in value
4. (adj)flat, monotone, monotonic, monotonous sounded or spoken in a tone unvarying in pitch "the owl's faint monotonous hooting"