What is timbre as a common element of music in the type of which govern melody and harmony?

In music, timbre is the quality of a musical note, sound, or tone that distinguishes different types of sound production, such as voices and musical instruments, string instruments, wind instruments, and percussion instruments. 

In simple terms, timbre is what makes a particular musical sound different from another, even when they have the same pitch and loudness. 

Hope that helped!! :)

nope! and if it is, i'd rather not know lol