Gannets are seabirds comprising the genus Morus, in the family Sulidae, closely related to boobies. "Gannet" is derived from Old English ganot, ultimately from the same Old Germanic root as "gander".

What does gannet mean in slang?

slang a gluttonous or greedy person.

Where does the expression gannet come from?

"Gannet" is derived from Old English ganot, ultimately from the same Old Germanic root as "gander". Morus is derived from Ancient Greek moros, "foolish", due to the lack of fear shown by breeding gannets and boobies, allowing them to be easily killed.