means A long speech delivered by one person, often uninterrupted, whether in a play, a film, or a conversation that has quietly become a one-way street.

from From Greek 'monologos,' stitching together 'monos' (alone, single) and 'logos' (speech, word, reason) — literally 'speaking alone.' It reached English through French in the 17th century, a sibling of 'dialogue,' where the 'dia-' (across, between) gives way to 'mono-,' and suddenly there's nobody to talk back.