Argonaut might rein in sheep, perhaps (7)
I believe the answer is:
mariner
'argonaut' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe there's an association between them I don't understand?
'might rein in sheep perhaps' is the wordplay.
'might' is an anagram indicator (I've seen this in other clues).
'in' is an insertion indicator.
'sheep perhaps' becomes 'mar' (I can't justify this - if you can you should give a lot more credence to this answer).
'rein' is an anagram of 'rine'.
'rine' placed within 'mar' is 'MARINER'.
Can you help me to learn more?
(Other definitions for mariner that I've seen before include "'''The Rime of the Ancient ...'' (Coleridge) (7)'" , "Seaman" , "Sailor" , "Man of the sea" , "collier?" .)