Tonelessly is an adverb that describes a lack of emotion or variation in a person's voice. There are several synonyms for tonelessly, including monotonously, expressionlessly, and flatly. Monotonously refers to a repetitive and unvarying tone, while expressionlessly suggests a lack of facial expressions as well as vocal variation. Flatly means without intonation or inflection and is often used to describe a statement that lacks emphasis or emotion. Other synonyms for tonelessly include lifelessly, blankly, and unemotionally. Whatever the chosen word, it is clear that a lack of tone can be just as important as the words themselves when it comes to communication.