edible type of spiny-finned fish, mid-15c., from Anglo-French molett (late 14c.), Old French mulet, from Medieval Latin muletus, from Latin mulettus, from mullus "red mullet," from Greek myllos a marine fish, related to melos "black" (see melanin).
"hairstyle short on top and long in back," 1996, perhaps from mullet-head "stupid, dull person" (1857). Also the name of a type of North American freshwater fish with a large, flat head (1866). The term in reference to the haircut seems to have emerged into pop culture with the Beastie Boys song "Mullet Head."
#1 on the side and don't touch the back
#6 on the top and don't cut it wack, Jack
[Beastie Boys, "Mullet Head"]
As a surname, Mullet is attested from late 13c., thought to be a diminutive of Old French mul "mule." Compare also mallet-headed, in reference to the flat tops of chisels meant to be struck with a mallet.