Many a creature seen in a wood (8)
I believe the answer is:
'a wood' is the definition.
(I know that mahogany is a type of wood)
'many a creature seen in' is the wordplay.
'creature' becomes 'hog' (hog is a kind of creature).
'seen in' is an insertion indicator.
'many' placed around 'ahog' is 'MAHOGANY'.
(Other definitions for mahogany that I've seen before include "Reddish-brown wood" , "Log" , "tree" , "Reddish-brown hardwood" , "Hogmanay? (anag)" .)