From est (“there is”) + ubi (“when, where”) referring to "time, opportunity".
est ubi (present infinitive esse ubi, perfect active fuit ubi); irregular conjugation, irregular, impersonal, no passive, no supine stem except in the future active participle
| Conjugation of est ubi (highly irregular, suppletive, no supine stem except in the future active participle, impersonal, active only) | |||||||
|---|---|---|---|---|---|---|---|
| indicative | singular | plural | |||||
| first | second | third | first | second | third | ||
| active | present | — | — | est ubi | — | — | — |
| imperfect | — | — | erat ubi | — | — | — | |
| future | — | — | erit ubi | — | — | — | |
| perfect | — | — | fuit ubi | — | — | — | |
| pluperfect | — | — | fuerat ubi | — | — | — | |
| future perfect | — | — | fuerit ubi | — | — | — | |
| subjunctive | singular | plural | |||||
| first | second | third | first | second | third | ||
| active | present | — | — | sit ubi | — | — | — |
| imperfect | — | — | esset ubi, foret ubi |
— | — | — | |
| perfect | — | — | fuerit ubi | — | — | — | |
| pluperfect | — | — | fuisset ubi | — | — | — | |
| imperative | singular | plural | |||||
| first | second | third | first | second | third | ||
| active | present | — | — | — | — | — | — |
| future | — | — | estō ubi | — | — | — | |
| non-finite forms | active | passive | |||||
| present | perfect | future | present | perfect | future | ||
| infinitives | esse ubi | fuisse ubi | futūrum esse ubi, fore ubi |
— | — | — | |
| participles | — | — | futūrus ubi | — | — | — | |