Trod again, changing step (9)
I believe the answer is:
gradation
'step' is the definition.
(synonyms)
'trod again changing' is the wordplay.
'changing' indicates anagramming the letters.
'trod'+'again'='trodagain'
'trodagain' with letters rearranged gives 'GRADATION'.
(Other definitions for gradation that I've seen before include "Spoil" , "Scale of successive changes or stages" , "Change of tone" , "series of changes" , "Degree, step" .)