Definition of lubricant noun from the Oxford Advanced Learner's Dictionary

lubricant

noun
ˈluːbrɪkənt
 
; ˈluːbrɪkənt
 
(also informal lube
luːb
 
; luːb
 
)
[uncountable, countable]
 
a substance, for example oil, that you put on surfaces or parts of a machine so that they move easily and smoothly