Abarim Publications' online Biblical Hebrew Dictionary
זפת
The feminine noun זפת (zepet), meaning pitch, is a bit of an orphan. There is no associated verb extant in the Hebrew Bible, nor are there other words known that derive from a joined root. And so it is assumed that our word is a loan word from either Aramaic or Egyptian, but that's conjecture at best.
Our word occurs twice (or rather three times) in the Bible: In Exodus 2:3 we read how Jochebed covered a wicker basket with pitch, deposited Moses in it and set it among the reeds of the Nile.
The only other time our word is used (twice) is in Isaiah, where YHWH proclaims that the streams of Bozrah and Edom to be turned into pitch, and their land shall become burning pitch (Isaiah 34:9).
If this noun was a proper Hebrew word, it would have been derived from a verb. Perhaps this verb was of a similar meaning as כפר kpr, meaning to cover over or even to atone.