It runs its course (5)
I believe the answer is:
water
'course' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'it runs its' is the wordplay.
I cannot quite see how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is present in the answer.
'runs' could be 'r' (cricket abbreviation) and 'r' is found in the answer.
The remaining letters 'wae' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for water that I've seen before include "non-alcoholic drink" , "Essential liquid" , "Quality of diamonds" , "Irrigate" , "Transparent liquid" .)