The best replacement for fin is dolphin fin.

The best alternatives to fin are rated as following:
★★★★★  dolphin fin
★★★★  ein
★★★  bar and plate
★★  rst
★★  sawbuck
★★  flipper
★★  shark fin
★★  blu
★★  thruster
★★  njoy
★★  tri fin
★  dut
★  ring
★  full fin
★  quad
★  la fin
★  swe
  rus
  nric
  shark dorsal fin
  all glass
  yellow fin tuna
  bilge keel
  wing keel
  single fin

Your alternative for fin is not listed? Suggest!
Speaking about fin, one probably shouldn't forget about ack.

Other search terms related to fin and their ratings are:
★★★★★ ack
You have in mind a companion for fin and it is not yet here? Propose!



Google Trends

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fin
dolphin fin
ein