What is the meaning of "Gad G'dud 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: Ya'akov 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.
Seforno: After blessing Dan that he (Shimshon) would fight like a snake
What does the second half of the Pasuk mean?
Rashi: And they will all return (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 will fearlessly attach them, repelling them and forcing them to flee back to their land in disgrace. 3
Seforno: Refer to 49:19:1:4. "ve'Hu Yagud Akeiv"
To the portion of land on the east side of the Yarden that they asked for and received.
Ya'akov is praising Gad for their strength, as Moshe will do in v'Zos ha'Berachah (33:20), where he refers to the vast expanse of land that they inherited, that was constantly under attack by Amon and Mo'av, their wicked neighbors. See also Rashi there.
See also Ba'al ha'Turim.
Seforno: In keeping with the Pasuk in Mishpatim, Sh'mos 23:27.
רש"י: גדוד שם דבר צריך שני דלתי"ן: מה פרוש הדברים?
גור אריה: 'שם דבר' הוא עצם הדבר ועיקרו, ולכן התיבה נאמרת בשלמות. לעומת זאת ה'פועל' איננו עיקר הדבר ולכן כתוב "יגודנו" בלי כפל הדל"ת.
רש"י: וכשהוא מתפעל או מפעיל אחרים הוא כפול: למה הדבר כך?
גור אריה: בבנין מפעיל או מתפעל יש ריבוי פעולה ולכן התיבה נאמרת בשלמות, אבל בפועל קל תבוא התיבה חסרה.