Argonaut dropping gun parts off vessel (5)
I believe the answer is:
aorta
'off vessel' is the definition.
'aorta' can be an answer for 'vessel' (aorta is a kind of vessel). I am not sure about the 'off' bit.
'argonaut dropping gun parts' is the wordplay.
'dropping' is a deletion indicator.
'parts' indicates an anagram (the parts of the original word ordered differently).
'argonaut' with 'gun' removed is 'aroat'.
'aroat' anagrammed gives 'AORTA'.
Can you help me to learn more?
(Other definitions for aorta that I've seen before include "Vital blood vessel" , "sort of vessel" , "Main route from the heart" , "Major blood vessel" , "Tube" .)