Dictionary.com
Thesaurus.com

solidarize

American  
[sol-i-duh-rahyz] / ˈsɒl ɪ dəˌraɪz /
especially British, solidarise

verb (used without object)

solidarized, solidarizing
  1. to unite or come together; become solidified.


Etymology

Origin of solidarize

From the French word solidariser, dating back to 1885–90. See solidary, -ize