Smooth driver? (4)
I believe the answer is:
iron
This might be a double definition.
'smooth' is the first definition.
(to smooth down with an iron)
'driver?' is the second definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
Can you help me to learn more?
(Other definitions for iron that I've seen before include "inflexible > club" , "Main component of steel" , "Flatten; element" , "Very robust" , "Metal - press" .)