coaxial

adjective

1. having a common axis
   also coaxal
2. designating a compound speaker consisting of a smaller unit mounted within and connected with a larger one on a common axis: the smaller unit reproduces the higher frequencies, beyond the range of the larger
3. ☆ designating a high-frequency transmission line or cable in which a solid or stranded central conductor is surrounded by an insulating medium which, in turn, is surrounded by a solid or braided outside conductor in the form of a cylindrical shell: it is used for sending telephone, telegraph, television, etc. impulses