hydraulic oil; hydraulic fluid
Technical term for the working fluid in hydraulic systems, used in machinery and industrial equipment.
This machine is leaking hydraulic fluid, so it needs immediate repair.
Please change the hydraulic oil regularly.
hydraulic oil; hydraulic fluid
Compound of 作動 (operation, activation) and 油 (oil), literally 'operation oil'. The exact historical derivation is uncertain, but the term is a straightforward modern technical coinage.