WordNet sense 1 ((physics) the force of attraction between all masses in the universe; especially the attraction of the earth's mass for bodies near its surface):

gravitation, gravitational attraction, gravitational force

WordNet sense 2 (a solemn and dignified feeling):

solemnity

WordNet sense 3 (a manner that is serious and solemn):

graveness, soberness, sobriety, somberness, sombreness