Too smooth for oil on troubled waters (5)
I believe the answer is:
slick
This might be a double definition.
'too smooth' is the first definition.
'slick' can be an answer for 'smooth' (slicking is a kind of smoothing). I'm not sure about the 'too' bit.
'oil on troubled waters' is the second definition.
'slick' can be an answer for 'oil' (thesaurus). I am unsure of the 'on troubled waters' bit.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for slick that I've seen before include "Smart" , "it's very oily" , "Bedeck" , "polished performance" , "Sleek - film of oil" .)