Small crown for one in farewell (5)
I believe the answer is:
tiara
'small crown' is the definition.
(I've seen this in another clue)
'one in farewell' is the wordplay.
'one' becomes 'I' (Roman numeral).
'in' indicates putting letters inside.
'farewell' becomes 'ta-ra' (both can mean goodbye).
'i' put within 'tara' is 'TIARA'.
'for' is the link.
(Other definitions for tiara that I've seen before include "Half-crown?" , "Ornamental headpiece" , "Jewelled headband" , "High diadem" , "Jewelled headpiece" .)