a combining form meaning “loin,” used in the formation of compound words: lumbosacral.
Also especially before a vowel, lumb-.
Origin of lumbo-
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
word-forming element meaning "loin, loins," from comb. form of Latin lumbus (see lumbago).
Online Etymology Dictionary, © 2010 Douglas Harper