1) flap-like external organ concerned with locomotion in fishes. See dorsal, adipose, caudal, anal, pelvic (ventral), and pectoral fins2) an arm or hand (slang). See also tip the fin3) in America a $5 bill, from the Yiddish finnif, a ₤5 note in England in the nineteenth century. From the German funf or five4) the verb for the process known as finning
Dictionary of ichthyology. 2009.