Pulled — hard — leg of the setter about taxonomic term (8)
I believe the answer is:
'taxonomic term' is the definition.
'pulled hard leg of the setter about' is the wordplay.
'pulled hard' becomes 'taut'.
'leg' becomes 'on' (cricket term, fielding positions).
'of the setter' becomes 'my' (belonging to the person who set the crossword).
'about' shows that the letters should be reversed in order.
'my' written backwards gives 'ym'.
(Other definitions for tautonym that I've seen before include "Name such as Bufo bufo or Anser anser" , "A scientific name in which the same word is used for both genus and species; to my aunt (anag.)" .)