One of the mysteries of the English language finally explained.
Engineering. A ring or chain which dips into an oil reservoir and continuously lubricates a shaft or bearing around which it revolves. Also: a piston ring serving to prevent leakage of lubricants from the cylinder.
Mid 19th century; earliest use found in Engineering. From oil + ring.
oil ring/ˈɔɪl rɪŋ/
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