tone of voice; manner of speaking
Refers to the overall quality, pitch, rhythm, or emotional coloring of speech, not just the words themselves. Often used when describing how something is said.
His tone of voice was very gentle.
Please don't speak in an angry tone.
She spoke in a gentle tone of voice.
His tone of voice suddenly changed when he was scolded.
The teacher warned him with a slightly sharper tone of voice.
調子 is a broader word for tone, condition, or rhythm that can apply to speech or many other things, while 口調 is used specifically for how someone's voice sounds when talking.
口調 focuses narrowly on the tone or rhythm of speech, while 口ぶり also implies the speaker's underlying attitude or intention that can be inferred.
口調 emphasizes the rhythm and manner of speaking, while 声色 focuses on the actual tone or quality of the voice.
口調 focuses on the rhythm, pitch, or flow of speech, while 語気 emphasizes the emotional attitude or force behind the words.
口調 focuses narrowly on tone of voice and intonation, whereas 語り口 covers the overall narrative delivery, pacing, and phrasing.
口調 refers narrowly to the tone or intonation of someone's speech, while 話しぶり covers the whole manner and style of speaking.
口調 focuses narrowly on tone of voice, whereas 物言い covers both wording and attitude in how someone speaks.
口調 refers to the tone or intonation of speech, while 言葉遣い is about which words and expressions one chooses to use.
Compound of 口 (mouth, speech) and 調 (tune, tone). The combination naturally yields 'tone of voice'.