mersister

noun

1. A sister who is a mermaid.

   “In the 2008 Broadway version of The Little Mermaid, the song, by Alan Menken (music) and Howard Ashman (lyric), was also performed by the mermaids (or mersisters).”

   “Remember, these are the people who kidnapped us and were going to cut out mine^([sic]) and my mersisters' vocal cords!”

   “Now that the mersisters were gone, that seemed more important than ever.”