Leeks are an onion and the name once captured the whole family. The older English leac referred to many kinds of onions or leeks, including the smallest member garleac. The gar means spear and references the pointed shape of the cloves. With today’s spelling it’s easier to notice their connection by saying them both aloud, leek and garlic.
Our onion is also a close cousin with union, both words from Latin unio. It means oneness, and names the onion for its inherent singularity despite it’s many layers. We use that name for onion in English and oignon French, but other languages find a different root.
Latin’s other onion name was cepa. That birthed the modern Spanish and Italian, cebolla and cipolla. Although oneness is the idea behind onion’s other root, the German word became zwiebolla during it’s evolution, suggesting two balls or duality.
The cepa root is also the less obvious source for shallots and scallions. The full name was cæpa Ascalonia or onion from Ascalonia. That place is still around today under the guise of Ashkelon, Israel, a coastal town just south of Tel Aviv. Both shallots and scallions went through French to get to English, with shallots picking up an -otte ending to make it a small onion.
Harder to see but the onion-like herb chives is another grandchild of cepa, from the French cive.
the journal of gastroetymology 