He helps things to go smoothly (5)

I believe the answer is:

oiler

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'he helps things to go smoothly' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

This is the entire clue.

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(Other definitions for oiler that I've seen before include "Chippendales assistant?" , "It carries fuel" , "One applying lubricant" , "it may be 4 [SHIPSHAPE]" , "If not well" .)

I've seen this clue in the Evening Standard.

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