One tweeting of passion in sport (8)
I believe the answer is:
wheatear
'one tweeting' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'passion in sport' is the wordplay.
'passion' becomes 'heat' (synonyms).
'in' means one lot of letters goes inside another.
'sport' becomes 'wear' (sport can mean to wear or display on one's person).
'heat' inserted inside 'wear' is 'WHEATEAR'.
'of' is the link.
Can you help me to learn more?
(Other definitions for wheatear that I've seen before include "Songbird" , "bird" , "singer" , "Migrant's passion" .)