time an entity begins to exist or a statement starts being valid
- from
- starting
- began
- from time
- since
- from date
- building date
- starttime
- introduced
- introduction
- started in
- beginning
- join date
- join time
- start date
- joined
- effective
- effectivity
- valid
- validity
- first air date
- air date
- first broadcast date
- broadcast date
- began airing
- began broadcasting
- began streaming
