If something such as a treatment is painless it causes no physical pain.
Acupuncture treatment is gentle, painless, and relaxing.
针灸治疗温和,无痛,令人放松。
The operation itself is a brief, painless procedure.
手术本身是一个短暂、无痛的过程。
If a process or activity is painless, there are no difficulties involved, and you do not have to make a great effort or suffer in any way.
The journey is relatively painless, even with children.
这趟旅程相对轻松,即使是带着孩子。