Part taken on board? (5)
I believe the answer is:
piece
'part' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for piece that I've seen before include "Chessman; portion" , "King, perhaps" , "Bit - part" , "Section; firearm" , "One part of a whole" .)