אָפּ 1
'off; down (adverb)'

ETYMOLOGY

Why is the consonant devoiced /p/?
Got. af, ON af, OE æf, of, OS af, OHG aba, ab. Cf. Latin ab, Greek ἀπό, Sanskrit āpa, Old Church Slavonis по 'after'

WESTERN

Old Literary Yiddish (ca. 1100-1800)

אונ' איז אלז אין אים הין אונ' ווידר גילאפֿן אויף אונ' אב
'and ran constantly back and forth in him up and down'