[as yiddish words] How about "gunsel" meaning gunman?
How about "shiv" meaning knife as weapon?

Disagree, dr. bill. AHD lists "shiv" as probably Romany, and mentions no possibility of a yiddish source. My old Websters agrees.

"Gunsel" could be argued as evidencing that yiddish lacks of a term for "gunman", forcing the yiddish speaker to coin one from the english word and a yiddish ending.

But that raises a conceptual point: when speakers of a language (in this case Yiddish) borrow from other languages, at what point do you say the borrowed term has passed into the borrowing tongue. For example, when a yiddish speaker says donton (meaning "downtown"), is he saying an english word (in his yiddish accent) or has it become an english word?

The question is particularly apt regarding Yiddish because (perhaps because its speakers were geographically dispersed in many lands, and were not generally the educated literate class), Yiddish borrowed heavily from other languages:

Yiddish, "the Robin Hood of languages," has practiced the most bouyant banditry among the words of every land in which its practitioners wandered. In the course of twenty-four hours, a son of Judah, speaking Yiddish today, may, without being aware of it, raid over two dozen other languages. Leo Rosten, Treasuty of Jewish Quotations (1972), p. 24.