The Collaborative International Dictionary of English v.0.48:

Grouper \Group"er\, n. [Corrupted fr. Pg. garupa crupper. Cf.
   Garbupa.] (Zool.)
   (a) One of several species of valuable food fishes of the
       genus Epinephelus, of the family Serranid[ae], as the
       red grouper, or brown snapper (Epinephelus morio), and
       the black grouper, or warsaw (Epinephelus nigritus),
       both from Florida and the Gulf of Mexico.
   (b) The tripletail (Lobotes).
   (c) In California, the name is often applied to the
       rockfishes. [Written also groper, gruper, and
       trooper.]
       [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Triple-tail \Tri"ple-tail`\, n. (Zool.)
   An edible fish (Lobotes Surinamensis) found in the warmer
   parts of all the oceans, and common on the southern and
   middle coasts of the United States. When living it is silvery
   gray, and becomes brown or blackish when dead. Its dorsal and
   anal fins are long, and extend back on each side of the tail.
   It has large silvery scales which are used in the manufacture
   of fancy work. Called also, locally, black perch,
   grouper, and flasher.
   [1913 Webster]

WordNet (r) 3.0 (2006):

grouper
    n 1: flesh of a saltwater fish similar to sea bass
    2: usually solitary bottom sea basses of warm seas