פּול
דער
'dust (collective)'

ETYMOLOGY

[Why Yiddish /u/ instead of /i/? Perhaps a hypercorrection on the border area between CY and NEY and SEY? See Herzog's map below.]
Herzog suggests פּול is from Belarusian.
Polish pył; Belarusian пыл; Ukrainian пил; cf. Russian пыль; from Proto-Slavic ✱pylъ.