As a Verb or Adjective:
1. To be the thing, person, event or period of time that happens or comes before all the others of the same kind. English = (be) first.
2. To be the first of a kind of thing to have ever existed, to be genuine and not a copy. English = (be) original.
3. To be in a state or condition of having had nothing changed or altered since it was first created. English = (be) original.
As Modifier:
1. Used immediately next to a verb to mean the action is done before anyone else or anything else does it. English = first.
2. Used at the beginning of a sentence when you are about to mention several things (events, reasons, etc.). English = first, firstly, first of all.