1. （尤用于机械的）润滑剂，润滑油
A lubricant is a substance which you put on the surfaces or parts of something, especially something mechanical, to make the parts move smoothly.

2. （比喻有利于事情顺利进行的）润滑剂
If you refer to something as a lubricant in a particular situation, you mean that it helps to make things happen without any problems.

1. a substance capable of reducing friction by making surfaces smooth or slippery

Synonym: lubricatorlubricating substancelube