caudal fin
US /ˈkɔːdəl fɪn/
UK /ˈkɔːdəl fɪn/
1.
the tail fin of a fish or other aquatic vertebrate
:
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The shark's powerful caudal fin propelled it through the water.
•
Fish use their caudal fin for propulsion and steering.
the tail fin of a fish or other aquatic vertebrate