Venison: age, roast while turning, infused with herb (7)
I believe the answer is:
oregano
'herb' is the definition.
(I know that oregano is a type of herb)
'venison age roast while turning infused with' is the wordplay.
'infused with' indicates a hidden word.
'turning' shows that the letters should be reversed in order.
'onagero' is hidden within 'venison age roast while'.
'onagero' backwards is 'OREGANO'.
(Other definitions for oregano that I've seen before include "leaves for season" , "that's aromatic" , "Pungent seasoning leaves" , "Herb - a no-goer (anag)" , "Herb used in cookery" .)