sed-

Etymology
*s(w)ēd, the ablative singular of lengthened under phrasal stress. Original form preserving the inherited /d/, which has been reinterpreted as hiatus-filler, but lost otherwise in all cases of long vowel preceding final /d/, such as other ablatives.

as well as, where the vowel shortened (or never lengthened).

Usage notes

 * Appears in just one base - cf. in.