Origin

The character combines the mouth radical 口 with 垂, which means to hang or droop. Since saliva is a liquid that hangs or drips from the mouth, the two components together create a visual metaphor for this bodily fluid. The drooping component suggests the motion of saliva falling or hanging down, while the mouth component makes clear this is something that comes from the mouth. This combination of meanings captures both where saliva comes from and how it behaves.