Other forms: coalesced; coalescing; coalesces
Waiting for a plan to come together? You're waiting for it to coalesce. Coalesce is when different elements of something join together and become one.
In coalesce, you see co-, which should tell you the word means "together." The other half of the word comes from alescere, a Latin verb meaning "to grow up." So if you are trying to start up a photography club at school, once you have an advisor, some interested students, and support from the administration, things will hopefully coalesce, or come together, to make it happen.