An Etymological Dictionary of the German Language/Eiter
Eiter, n., ‘pus, matter, suppuration,’ from MidHG. eiter, OHG. eitar (eittar), n., ‘poison’ (especially animal poison); Goth. *aitra- is wanting; an old tr remains unchanged in HG. (see treu, zittern). Comp. MidLG. and Du. etter, AS. âttor, attor, E. atter (‘pus, poison’), OIc. eitr, n. Also a variant without the suffix r (Goth. *aita-); comp. OHG. and MidHG. eiȥ (Alem. eisse, Bav. aiss), m., ‘abscess, ulcer,’ with a normal permutation of t to ȥȥ. The Teut. root ait, ‘poisonous ulcer,’ has been rightly connected with the Gr. οἶδος, n., οἶδμα, n., ‘swelling,’ οἰδάω, ‘to swell’; hence the root is Aryan oid.