Part of speech: conjunction, relative pronoun
1. that; 2. which; that; who; 3. because, for
[← þata demonstr pron + -ei rel part]
þatei - Matth. V, 20; V, 21; V, 22; V, 23; V, 27; V, 28; V, 31; V, 32; V, 33; V, 38 etc
jaþ-þatei = jah (vid jah cj) + þatei - Cor. I, XV, 4; XV, 5

3.6. Relative pronouns

Relative pronouns in Gothic are derived by means of the addition of the part -ei to the demonstrative pronouns: saei (who, that, which) (masc), þatei (which; that) (neut) and soei (who, that, which) (fem). This derived form is declined in the same way as the plain demonstr pron, with the part -ei being added to the case endings of the demonstr pron in question. cf masc, Nom saei, Gen þizei, Dat þammei, Acc þanei, etc; fem, Nom soei, Gen þizozei, Dat þizaiei, Acc þoei etc rel pron-s saei, þatei, soei are often used in Gothic, introducing subordinate clauses.

Alongside masc sing Nom saei, Gothic often uses the form izei (< pers pron is (3 pers, sing, masc) + part -ei). izei was often used in subordinate clauses as a kind of petrified relative pronoun; cf þaim izei qimand at izwis ((those) who come to you( (Matth. 7:15); niu mahta sa izei uslauk augona þamma blindin ... (could not this man, who opened the eyes of the blind …) (Jhn. 11:37). Similarly, alongside rel pron soei (fem sing Nom) there is used rel pron sei (< pers pron si (3 pers, sing, fem) + part -ei). Remarkably, sei is used exclusively in Nom, sing.