Romanian word fost comes from Proto-Indo-European *h₁ésti (To be.), Proto-Indo-European *h₁ésmi, Proto-Indo-European *bʰowHéyeti, Proto-Indo-European - -yéti
| Dictionary entry | Language | Definition |
|---|---|---|
| *h₁ésti | Proto-Indo-European (ine-pro) | To be. |
| *h₁ésmi | Proto-Indo-European (ine-pro) | |
| *bʰowHéyeti | Proto-Indo-European (ine-pro) | |
| - -yéti | Proto-Indo-European (ine-pro) | |
| *som | Proto-Italic (itc-pro) | |
| *ezom | Proto-Italic (itc-pro) | Be. |
| *bʰuHyéti | Proto-Indo-European (ine-pro) | To be becoming, to be growing, to be appearing. |
| esom | Old Latin (itc-ola) | |
| *fuiō | Proto-Italic (itc-pro) | To become. |
| fiere | Latin (lat) | |
| *fio | Latin (lat) | (Vulgar Latin, Eastern Romance and Italy) I am. |
| fui | Latin (lat) | |
| *sun | Latin (lat) | (Vulgar Latin) I am. |
| fi | Romanian (ron) | To be. |
| fost | Romanian (ron) | Ex-boyfriend. |