例子:
I was terrified when I saw a fin just behind Mickey, who was swimming far away from the beach. I knew it was a shark, and it looked big. 
照片许可:
CC版权：出处标示，商业用途
Regionalism:
Neutral
Regional variant:
Neutral
Full Expression:
The “in” Sound ( /ŋ/ + /g/ ) : fin
the triangle-shaped upper part of a shark, dolphin, or similar animal, which is exposed above the water line when the animal is swimming close to the surface