monotone (Adjective) — Sounded or spoken in a tone unvarying in pitch. ex. "the owl's faint monotone hooting"
monotone (Adjective) — (mathematics) of a sequence or function; consistently increasing and never decreasing or consistently decreasing and never increasing in value.
monotone (Noun) — An unchanging intonation.
monotone (Noun) — A single tone repeated with different words or different rhythms (especially in rendering liturgical texts).