The following information is taken from the Dictionary of the Older Scottish Tongue, available online at http://www.dsl.ac.uk/index.html. This is a work in progress.
| Spelling | Number | Dates & headers |
|---|---|---|
| Foster | 4 | 1488 (bygane, count); 1566 (counsallschip); 1644 (col-) |
| Fosster | 1 | 1459 (annuel) |
| Fostar | 1 | 1461 (award) |