Post office work aboard ship? (4)

I believe the answer is:

poop

I'm a little stuck... Click here to teach me more about this clue!

'ship?' is the definition.
(thesaurus)

'post office work aboard' is the wordplay.
'post office' becomes 'po'.
'work aboard' becomes 'op' (common abbreviation for 'opus'. I am not sure about the 'aboard' bit.).
'po'+'op'='POOP'

Can you help me to learn more?

(Other definitions for poop that I've seen before include "Tony" , "raised structure" , "High deck at old sailing ship's stern" , "Palindromic part of a ship" , "Raised stern of a sailing ship" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.