What is the definition of "M'sim"?
Rashi, Targum Onkelos and Targum Yonasan: ?M?sim? is 'Men'.
What is the translation of "es Kol Ir M'sim, ve'Nashim ve'Taf"
Oznayim la'Torah: It means the entire town of men, women and children'. 1
And not 'the entire town, the men, the women and the children', because they were not commanded to destroy the towns. See Oznayim la'Torah here and on 3:6. The Trop on "Ir M'sim" also supports this explanation.
Why does the Torah write here "Bazaznu" and in Va'eschnan, 3:7 - in connection with Og - "Bazonu" (with only one 'Zayin')?
Rashi: Because the vast amounts of spoil that they took from Sichon left them satiated. Consequently, they approached the spoil of Og with a degree of contempt, 1 discarding the animals and the clothes, taking only the silver and the gold. 2
"Bazonu" stems from the word 'Bizuy'.
This is difficult however, since, following the subsequent battle with Midyan, the Torah writes "asher Baz'zu Am ha'Tzava" - Mas'ei Bamidbar, 31:53. See Oznayim la'Torah on 3:7.
Why did they kill the women and children?