A Lantsman! (1970)

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THE TASTE OF YIDDISH
by Lillian Mermin Feinsilver
South Brunswick, NY: Thomas Yoseloff
1970

Pg. 202:
   A LANTSMAN!
   A countryman! (discovery that someone comes from the same part of the world that you do)
   Though originally this referred to the Old World, second- and third-generation American Jews use it good-humoredly.  Two New Yorkers meeting in Paris, for instance, might chuckingly use the exclamation.