Crossword Genius

More slick, having previously spoken in the Bronx? (6)

Ross

I believe the answer is:

oilier

'more slick' is the definition.
(slick can mean oily)

I don't understand how the rest of the clue works.

(Other definitions for oilier that I've seen before include "rather greasy" , "More lubricated or flattering" , "More oleaginous" , "having applied more sun cream?" , "More viscous or slippy" .)

I've seen this clue in The Guardian.
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