WordNet sense 1 (a hard lump produced by the concretion of mineral salts; found in hollow organs or ducts of the body):

calculus

WordNet sense 2 (an increase in the density of something):

compression, compaction, densification

WordNet sense 3 (the union of diverse things into one body or form or group; the growing together of parts):

coalescence, coalition, coalescency, conglutination