Dorsal and Dorsal fin

Dorsal adjective - Belonging to or on or near the back or upper surface of an animal or organ or part.

Dorsal fin and dorsal are semantically related. In some cases you can use "Dorsal fin" instead a noun "Dorsal".

Dorsal fin noun - Unpaired median fin on the backs of fishes and some other aquatic vertebrates that help to maintain balance.

Dorsal and dorsal fin are semantically related. You can use "Dorsal" instead a noun phrase "Dorsal fin".