How does one translate "Zeved" (and "Zevadani"), which has no parallel anywhere in Tanach?
Ramban #1: It is made up of two words - 'Zeh Bod' 3 (this is a branch), a term that is used here to describe children.
Ramban #2: It is as if the word was written with a 'Vav' (instead of a 'Veis' - which are in fact, interchangeable; he gives a number of examples of this). Le'ah meant that Hashem had given her good provisions and a good portion, for now her husband would live mainly with her. Refer to 30:20:2:1.
The Ramban gives a number of examples of words that are in fact, a corruption of two words.
What made Le'ah think that, following the birth of Zevulun, Ya'akov would make her his main wife?
Tosfos ha'Shalem (7): The three pillars of the world come from her children - Avodah from Levi, Torah from Yisachar, and Chesed from Zevulun (he fed Yisachar).
Why is Zevulun written lacking [the first] Vov?
Tosfos ha'Shalem (7): Leah lacked only six (the Gematriya of Vov) of the Shevatim that would be born.