mass

The quantity of matter an object contains, determining its inertia.

"The planet's mass affects its gravity."

To gather or form into a large body or group.

"Protesters began to mass outside the building."

The Christian Eucharist, especially a Roman Catholic Church service.

"They attended Sunday Mass at the local church."

A large quantity or collection of something, often without definite shape.

"A mass of dark clouds gathered quickly."