The word onion is derived from the Latin word 'unio' which means what?

This was a tough one to find..

From http://www.dictionary.com/browse/onion?s=t...

onion - 1130, from Anglo-Fr. union, from O.Fr. oignon, from L. unionem (nom. unio) 'a kind of onion,' also 'pearl,' probably the same word as unio 'one, {unity;'} sense connection is the successive layers of an onion, in contrast with garlic or cloves. O.E. had ynne (in ynne-leac), from the same L. source. Onions, the surname, is attested from 1159 (Ennian), from O.Wesh Enniaun, ult. from L. Annianus, which was associated with Welsh einion 'anvil.'