Or from Latin baculum a stick, because the squire would practice with a staff, not a sword. Meaning evolved from knight in training to young unmarried man (early 14c.). Bachelor party as a pre-wedding ritual is from 1882.
A transcutaneous electrical nerve stimulation (TENS) unit is a device that sends small electrical currents to targeted body parts. These currents are used to relieve pain. Some TENS units are designed for use in a hospital or healthcare facility.
Sorry he's having so much pain. The reason that you should NOT use a TENS unit or have ultra sound when you have mets is because it stimulates and causes cell growth for healing. But it can't tell the difference between the good and bad cells so it also can stimulate cancer cells.