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.
Oznayim la'Torah (citing the Midrash): It means 'fertilizer' ('Zevel'). Because Zevulun would fertilize Yisachar's field (Torah) to ensure that it produces fruit.
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). Leah 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 Leah think that, following the birth of Zevulun, Yaakov 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).
Malbim: Now that I have six sons, there is no room in my tent. Yaakov will need to take me into his tent!
Ha'amek Davar: The Shechinah dwells among 10. The majority helps much. 3 Therefore he will want to dwell in her tent.
Daf Al ha'Daf (Megilah 14a): Regarding what concerned them, all the Imahos were prophets.
If there were 10, and the majority prayed, this permits Chazaras ha'Shatz (or to finish saying it, if some left and the majority remained - MB 69:8, OC 55:3). However, the [10 and] six must be adults! Perhaps Leah meant that when her sons mature, he will accompany her. Or, since Shechinah will dwell in her tent, he will accompany her now. (PF)
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.