A preterite (/ˈpretəraɪt/) is the form of the verb used by itself in the past tense.
Full modal verbs have preterites too, e.g. "could" is the preterite of "can".
The preterite is not used with auxiliary do (preterite: did); rather a bare infinitive is used instead, as a second grammatical marker is not necessary. e.g. "I ate a sandwich" "I did eat a sandwich".