means A bar of metal, wood, or other material laid as a barrier or track — or, as a verb, to complain or protest bitterly.

from The noun comes from Old French 'reille' (a bar or rod), from Latin 'regula,' a straight stick or rule — the same root that gives us 'regulate' and 'rule.' The verb 'to rail' is a separate arrival, from Old French 'railler,' to mock or jest, which is why you can rail against something and stand on something with the same four letters and no shared blood.