WordWeb Online

1. (mathematics) of a sequence or function; consistently increasing and never decreasing or consistently decreasing and never increasing in value
   - monotone, monotonous
    
2. Sounded or spoken in a tone unvarying in pitch
   "the owl's faint monotonic hooting";
   - flat, monotone, monotonous

See also: decreasing monotonic, increasing monotonic, unmodulated

Encyclopedia: Monotonic