Retroaction not oddly one to inspire (5)
I believe the answer is:
erato
'one to inspire' is the definition.
(one of the Greek muses)
'retroaction not oddly' is the wordplay.
'not oddly' means one should take alternating letters (odd letters are removed).
The alternate letters of 'retroaction' are 'ERATO'.
(Other definitions for erato that I've seen before include "poetic patroness" , "One inspiring" , "Muse of lyric poetry and mime" , "verses she inspired" , "poetical inspiration" .)