Monotone
Part of speech: verb
Definition: To speak in a monotone.
Part of speech: adjective
Definition: having a single unvaried pitch property of a function to be either decreasing or increasing
Part of speech: noun
Definition: A single unvaried tone of speech or a sound
Droning
Part of speech: verb
Definition: To kill with a missile fired by unmanned aircraft.
Part of speech: noun
Definition: a dull humming