By-pass closed about mid-morning (5)
I believe the answer is:
shunt
'by-pass' is the definition.
Both the answer and definition are singular nouns.
Perhaps they are linked in a way I don't understand?
'closed about mid-morning' is the wordplay.
'closed' becomes 'shut' (synonyms).
'about' is an insertion indicator.
'mid' says to take the centre (mid- can mean the middle of something).
The middle letter of 'morning' is 'n'.
'shut' going around 'n' is 'SHUNT'.
Can you help me to learn more?
(Other definitions for shunt that I've seen before include "Car crash (slang)" , "Vehicle accident" , "Type of road accident" , "Move railway wagons etc" , "Arrange wagons; minor accident" .)