Own American writer’s story, primarily about steamship (7)
I believe the answer is:
possess
'own' is the definition.
(I know that own can be written as possess)
'american writer's story primarily about steamship' is the wordplay.
'american writer's' becomes 'poe's' (Edgar Allan Poe).
'primarily' suggests taking the first letters.
'about' means one lot of letters goes inside another.
'steamship' becomes 'ss' (nautical abbreviation).
The initial letter of 'story' is 's'.
'poes'+'s'='poess'
'poess' going around 'ss' is 'POSSESS'.
(Other definitions for possess that I've seen before include "Own, keep" , "Have as one's own" , "influence" , "Have and hold" , "Have - control" .)