What is a four letter verb for voice melody?

There isn't a common four-letter verb that specifically means "voice melody". However, depending on the context, you could use these:

* Sing: This is the most direct option, as singing is the act of producing a melody with the voice.

* Hum: This suggests a simple, quiet melody.

* Chirp: This implies a light, cheerful melody.

* Wail: This suggests a mournful or emotional melody.

Ultimately, the best verb depends on the specific melody you're describing.