collision /-lizhˈn/ noun

1. The state of being struck together
2. A violent impact, a crash
3. Conflict
4. Opposition
5. Clashing

collision course noun

A course which, if persisted in, will result in a collision (lit and figurative)

elastic collision

1. A collision in which both kinetic energy and momentum are conserved (physics)
2. A collision in which the bombarding particle does not excite or break up the struck nucleus, and is simply scattered, the process being termed elastic scattering (nuclear industry)

inelastic collision

1. A collision in which momentum, but not kinetic energy, is conserved (physics)
2. A collision in which there is a change in the total energies of the particles involved, the resultant scattering being termed inelastic scattering (nuclear industry)