monotonic
adjective uk/ˌmɒn.əˈtɒn.ɪk/ us/ˌmɑː.nəˈtɑː.nɪk/
(SOUND)
formal（说话的声音）缺乏抑扬顿挫的
speaking or spoken in such a way that the sound stays on the same note without going higher or lower
(QUANTITY)
mathematics specialized（数量）单一变化的（要么一直上升，要么一直下降）
(of a quantity) only ever increasing, or only ever getting less