A-þierran

According to the Old English Dictionary:

a-þierran

p. de; pp. ed To wash off or away, rinse, make clean, purge, clear; diluere :-- Hit is þearf, ðæt sió hond sié ǽr geclǽnsad, ðe wille ðæt fenn of óðerre aþierran necesse est ut esse munda studeat manus, quæ diluere sordes curat, Past. 13, 1 ; Hat. MS. 16 b, 8. a-þierran