flipper
noun [ C ] uk/ˈflɪp.ər/ us/ˈflɪp.ɚ/
(PART OF CREATURE)
（海豹、企鹅等海洋生物用来游泳的）鳍肢，鳍足
one of two parts like arms on the bodies of some sea creatures, such as seals and penguins, used for swimming
(SHOE)
(US also fin)（尤指潜水用的）橡皮脚掌，脚蹼，鸭脚板
a type of large, flat rubber shoe used for swimming, especially underwater