The term 'Scallion Kin' refers to three vegetables that are related to each other: LEEK (4 letters), ONION (5 letters), and Greenonion (10 letters). All three vegetables are members of the Allium genus, which includes onions, garlic, leeks, and shallots. Leeks are a milder version of onions, while greenonions are a type of ONION with a milder flavor and a more tender texture. Scallions, also known as green onions, are a type of ONION with a milder flavor and a more tender texture.