Finish transmitting without son (6)
I believe the answer is:
ending
'finish' is the definition.
(thesaurus)
'transmitting without son' is the wordplay.
'transmitting' becomes 'sending' (sending is a kind of transmitting).
'without' indicates named letters should be taken away.
'son' becomes 's'.
'sending' with 's' taken away is 'ENDING'.
(Other definitions for ending that I've seen before include "Concluding" , "Cessation" , "Final part" , "Closing down" , "Termination, conclusion" .)