First appearance of that word in the Bible was in Genesis 10:14, BTW, showing their lineage after the flood.
According to Strong’s Dictionary, the root of the word “pelesheth” is “palash”, literally meaning to wallow in the mud.
Don’t know any dictionaries, but in Talmudic parlance a “mavuy mfulash” means an alley that’s open on both sides, i.e. open to invasion. “Polshim” are people who poke around in the ground with sticks, looking for hidden caches of money or other valuables. In modern Hebrew “polshim” means home invaders. It might have concurrent meanings.