Origin

The character 墓 combines earth or soil (土) at the bottom with 莫 at the top, which serves as a sound hint for the pronunciation. Since a grave or tomb is fundamentally a place in the ground where the dead are buried, pairing the earth radical with a sound component makes sense — the shape tells you both what the word means (something to do with soil) and roughly how to say it. The 莫 component doesn't contribute its own meaning here, but rather guides speakers toward the correct pronunciation of this earth-related word.