1) All work and no play 2) Having very little inflection 3) Lacking in variety 4) Like a one-note performance 5) Monotone 6) Monotonic 7) Unmelodic 8) Unmelodious 9) Unmusical 1) Boring 2) Drab 3) Dull 4) Humdrum 5) One note 6) Ordinary 7) Singsong 8) Static 9) Tedious 10) Tiresome 11) Uninteresting 12) Unmelodic 13) Unvaried 
• (a.) Uttered in one unvarying tone; continued with dull uniformity; characterized by monotony; without change or variety; wearisome.
Mo·not'o·nous adjective [ Greek ...; 
monotonous Going on in the same tone without variation.
lacking in variety; tediously unvarying: the monotonous flat scenery. · characterizing a sound continuing on one note. · having very little inflection; limited to a narrow pitch range.
[SAT terms] sounded or spoken in a tone unvarying in pitch[Literary terms] sounded or spoken in a tone unvarying in pitch[Lexical terms] sounded or spoken in a tone unvarying in pitch[Difficult words] sounded or spoken in a tone unvarying in pitch[Obscure words] sounded or spoken in a tone unvarying in pitch