Send a Morse message or intercept one (3)
I believe the answer is:
tap
'intercept one' is the definition.
'tap' can be an answer for 'intercept' ('tap' can be a synonym of 'intercept'). I am not certain of the 'one' bit.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for tap that I've seen before include "1dn to get on the phone, perhaps!" , "Knock gently" , "Bugging device" , "Stopper enabling withdrawal of liquid" , "Thread cutter; strike" .)