Poison found in oven, ominously (5)
I believe the answer is:
venom
'poison' is the definition.
(I know that venom is a type of poison)
'in oven ominously' is the wordplay.
'in' indicates the answer is hidden within the clue.
'VENOM' is hidden within 'oven ominously'.
'found' is the link.
(Other definitions for venom that I've seen before include "Snake's poison" , "Snake poison" , "Poison; malice" , "essential part of The Sting" , "bitterness" .)