Possibly from Vulgar Latin *excomborāre, from a proposed Proto-Celtic *comboros. This could be from the same root underlying Medieval Latin combrus (“barricade of felled trees”), reconstructed as Gaulish *komberū, from Proto-Celtic *kombereti (“to bring together”) (from *kom- + *bereti (“to bear”)) and found in Medieval Latin incombrō, the source of Old French encombrer.