What is the meaning of "Gad Gedud Yegudenu"?
Rashi, Targum Onkelos and Targum Yonasan: The regiments of Gad will proceed to fight with their brothers on the other (west) side of the Yarden. 1
Ramban #1: Bands of brigands will frequently attack their land. 2
Ramban #2: Yaakov was referring to Yiftach ha'Gil'adi, whose territory included half of what had previously belonged to Amon, who consistently attempted to recapture it, until Yiftach defeated them in battle. 3
Ohr ha'Chayim #1: "Gedud" is an expression of a camp; 'Gediyah' of pulling and surrounding. Its enemies will surround Gad on his banks, and he will cut them off.
Ohr ha'Chayim #2: Gad's camp will increase.
Malbim: Gad will go at the front of Machaneh Yisrael. There will be two sets of troops. One is to fight the enemy; and refer to 49:19:2:6.
Ha'amek Davar: Gad dwelled in serenity and did not fear lest enemy troops surround it, and then it will not be able to leave. It let the enemy surround Gad... Refer to 49:19:2:7.
What does "v'Hu Yagud Akev" mean?
Rashi: ... And they will all return (i.e. without losing a man) the way they came. 1
Targum Onkelos and Targum Yonasan: They will return to their land 2 with a lot of property (spoil).
Ramban: '... And they [Gad] will fearlessly attack them, repelling them and forcing them to flee back to their land in disgrace.' 3
Ohr ha'Chayim #1: Gad will cut them off until they are finished.
Ohr ha'Chayim #2: Gad will surround all of Machaneh Yisrael and fight for them, until they inherit their full inheritance.
Malbim: There will be a second set of troops from Gad that goes at the [other] side [of the enemy, in ambush], in order to surround the enemy. It is called Akevo of the Machaneh, for it is Akev (tracks) to surround the enemy from two sides - as in the Pasuk, "ha'Machaneh Asher mi'Tzafon la'Ir v'Es Akevo" (Yehoshua 8:13).
Ha'amek Davar: After the enemy surrounded Gad, Gad would overpower and surround them.
To the portion of land on the east side of the Yarden that they asked for and received.
Yaakov is praising Gad for their strength, as Moshe will do in V'Zos Ha'Berachah (Devarim 33:20), where he refers to the vast expanse of land that they inherited - which was constantly under attack by Amon and Mo'av, their wicked neighbors. See also Rashi there.
See also Ba'al ha'Turim.
QUESTIONS ON RASHI
Rashi writes: "These are all expressions of the term 'Gedud' (a troop). But the word 'Gedud' has two letters Dalet (and why do 'Yegudenu' and 'Yagud' have only one)? When a two-letter root becomes a noun, we need to double the last letter.... and when a verb is reflexive or causative, we also double it." Why is this so?
Gur Aryeh: A noun means that something exists, its essence is expressed practically; therefore, its root is expressed in full with three letters. 1 A verb in simple form (Kal) indicates mere action, rather than essence; therefore two letters of the root suffice. 2 In an intensive verb, 3 the root must once again be expressed in full.
