The first lubricant to work (4)
I believe the answer is:
toil
'work' is the definition.
(I know that toil is a more specific form of the action the work)
'the first lubricant' is the wordplay.
'the first' becomes 't' (1st letter of 'the').
'lubricant' becomes 'oil' (I've seen this in another clue).
't'+'oil'='TOIL'
'to' is the link.
(Other definitions for toil that I've seen before include "Drudgery" , "Work extremely hard" , "Hard physical work" , "Manual labour" , "Work hard and long" .)