Line drawn when work is overshadowed by short ruse (6)
I believe the answer is:
tropic
'line' is the definition.
(tropic is a kind of line)
'drawn when work is overshadowed by short ruse' is the wordplay.
I cannot really understand how this works, but
'work' could be 'op' (abbreviation for opus) and 'op' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for tropic that I've seen before include "Line bordering hot region" , "Line of latitude determined by the solstice" , "Interzonal line" , "Line at nearly 23 degrees N or S" , "Latitude 23 and a quarter 26 N or S" .)