1. To cleave or to remain together; especially said of the constituent parts of a material substance: The glue seemed to stick, or to cohere, so well that the envelope would not open again. 
2. To hold together in a mass that resists separation: The ballet was so beautiful because all of the dancers were in exact timing and motion with each other and so they seemed to cohere into one united group.
3. When referring to people: to remain together; to unite or to stay united in some action: For the project, the students in the group cohered their ideas in order to produce a well organized and informative report about the migrating birds.
4. Etymology: borrowed from Latin cohaerere, "to cling together, to cleave together"; from co-, "together" + haerere, "to cling to, to cleave to (to hold together and to resist separation)".