To stick together physically, by adhesion.
To be consistent as part of a group, or by common purpose.
to join items together, or to coat them with solder
to join things as if with solder.
Any of various easily-melted alloys, commonly of tin and lead, that are used to mend, coat, or join metal objects, usually small.
Figuratively, circumstances or emotions that strongly bond things or persons together in analogy to solder that joins metals.