| 1 | Middle English | castle | Alternative form of castel |
| 2 | Middle English | castel | castle |
| 3 | Old English | castel | town; village; castle |
| 4 | Breton | kastell | castle |
| 5 | Italian | castello | castle |
| 6 | Latin | castellum | castle, fort, citadel, fortress, stronghold; a... |
| 7 | Latin | castrum | castle, fort, fortress; camp, especially a... |
| 8 | Proto-Italic | kastrom | knife |
| 9 | Proto-Indo-European | ḱos-tróm | — |
| 10 | Proto-Indo-European | ḱes- | to cut off, separate; to cut up, to slaughter; to... |