Complain bitterly about certain transport (4)
I believe the answer is:
rail
This might be a double definition.
'complain' is the first definition.
(I know that rail is a kind of complain)
'bitterly about certain transport' is the second definition.
The definition and answer can be both man-made objects as well as being singular nouns.
I also know that 'bitterly' relates to this answer.
Can you help me to learn more?
(Other definitions for rail that I've seen before include "transport system" , "wader" , "method of transport" , "Mode of transport; bar" , "British --; picture --" .)