Unpleasant smells that are very strong and not nice.
Stenches are usually bad because they make people feel sick or uncomfortable.
Examples:
The stenches from the garbage can were terrible.
I can't stand the stenches in this room.
The stenches of the old socks filled the room.
The stenches in the bathroom were so bad, I had to leave.
The stenches from the rotten eggs were unbearable.
The stenches in the haunted house were so scary.