Backache and Lumbar pain

Backache noun - An ache localized in the back.

Lumbar pain and backache are semantically related. In some cases you can replace phrase "Lumbar pain" with "Backache", this terms are similar.

Lumbar pain noun - Backache affecting the lumbar region or lower back; can be caused by muscle strain or arthritis or vascular insufficiency or a ruptured intervertebral disc.

Backache and lumbar pain are semantically related. You can use "Backache" instead a noun phrase "Lumbar pain".