くち口kuchiずさむzusamu
1.
To produce a melody softly, often with one's lips closed, expressing music or emotion without vocalizing lyrics fully.
2.
To lightly vocalize a tune or song, typically in a manner that indicates personal enjoyment or reflection.
3.
To engage in the spontaneous creation of lyrics or melodies, often expressing thoughts or feelings in an informal and improvised way.
Example:
母は台所でせっせと料理しながら歌を口ずさんでいた。