Rather upset, having swallowed one bone (5)
I believe the answer is:
tibia
'bone' is the definition.
(tibia is a kind of bone)
'rather upset having swallowed one' is the wordplay.
'rather' becomes 'abit' (I've seen this in other clues).
'upset' shows that the letters should be reversed in order.
'having swallowed' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'abit' reversed gives 'tiba'.
'tiba' placed around 'i' is 'TIBIA'.
(Other definitions for tibia that I've seen before include "Bone of the lower leg" , "Bone in osso bucco" , "ancient pipe" , "part of skeleton" , "Part of leg of" .)