lumbago vs lumbar pain

lumbago and lumbar pain both are nouns.

Word	Noun	Adjective	Verb	Adverb
lumbago	Yes	No	No	No
lumbar pain	Yes	No	No	No

As nouns, lumbago and lumbar pain are synonyms defined as:

lumbago and lumbar pain: backache affecting the lumbar region or lower back; can be caused by muscle strain or arthritis or vascular insufficiency or a ruptured intervertebral disc

lumbago (noun)	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 affecting the lumbar region or lower back; can be caused by muscle strain or arthritis or vascular insufficiency or a ruptured intervertebral disc