butterflyfish

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of various small tropical marine fishes of the family Chaetodontidae, having a laterally compressed body with bright colors and patterns.
• noun Any of various fishes with broad winglike fins.

from The Century Dictionary.

• noun The common name of the species of fishes of the family Chætodontidæ found in tropical seas, noted for their singular form, bright colors, and great activity. The family comprises 8 or 10 genera and nearly 200 species.
• noun An English name of the eyed blenny, Blennius ocellaris.—
• noun A fish of the family Nomeidœ, Gasterochisma melampus, with large black ventral fins, inhabiting the sea about Australia and New Zealand. It attains a length of more than 3 feet, but is rare.

from the GNU version of the Collaborative International Dictionary of English.

• noun tropical gurnardlike fish with huge fanlike pectoral fins for underwater gliding; unrelated to searobins.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any of a group of conspicuous tropical marine fish of the family Chaetodontidae; the bannerfish and coralfish are also included in this group. Butterflyfish are fairly small, mostly from 12 to 22 cm (c.7-9 in) in length.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun small usually brilliantly colored tropical marine fishes having narrow deep bodies with large broad fins; found worldwide
• noun tropical fish with huge fanlike pectoral fins for underwater gliding; unrelated to searobins