Smooth part of speech (4)
I believe the answer is:
roll
This might be a double definition.
'smooth' is the first definition.
(thesaurus)
'part of speech' is the second definition.
'roll' can be an answer for 'part' (thesaurus). I'm unsure of the 'of speech' bit.
Can you help me to learn more?
(Other definitions for roll that I've seen before include "directory" , "Register - for continental breakfast?" , "cylindrical moulding" , "Press" , "on which one is regularly successful" .)