I'm trying to determine the origin of the male first name "Jeko" as it belonged to one of my relatives >from Lublin, Poland but I have not so far met with success.
The rendering "Jeko" in Polish records is a common transcription error. The correct name is "Jcko" (pronounced Itsko) which is a Polish variant of the Hebrew name **Yitzchok** (Yiddish **Itsik**), commonly translated into English as Isaac.
