Upset as a result of cover-up over a long period (6)
I believe the answer is:
derail
'upset' is the definition.
The answer and definition can be both to do with motion as well as being verbs in their base form.
Perhaps there's an association between them I don't understand?
'a result of cover-up over a long period' is the wordplay.
'a result of cover-up' becomes 'dil' (I can't explain this - if you can you should believe this answer much more).
'over' indicates putting letters inside.
'a long period' becomes 'era' (I've seen this in another clue).
'dil' going around 'era' is 'DERAIL'.
'as' is the link.
Can you help me to learn more?
(Other definitions for derail that I've seen before include "create an obstructive diversion" , "stop things going smoothly" , "Cause to leave the tracks" , "put off track" , "Force off track, like a train" .)