Here's why and what you could do:
* Origin: Jillian is of Irish origin, meaning "youthful" or "downy-bearded".
* Polish Options:
* Closest Sound: You could use names that sound similar, like "Julianna" or "Julita".
* Meaning-Based: If you want a name with a similar meaning, you could use "Młoda" (young) or "Młodziutka" (very young), but these are more descriptive terms, not typical names.
* "Jilian" itself might be understood, but it wouldn't be a native Polish name.
It really depends on what you're looking for. Do you need a formal translation, a close sound-alike, or a name with a similar meaning?