The earliest known surviving records of Harwell's name are 10th-century Saxon charters now reproduced in the Cartularium Saxonicum. One from 956 records Horn Down, a nearby hill, as Harandúne, which is derived from the Old English for "grey hill". The same charter records the manor as Haranwylle, which comes from the Old English for "stream by or coming from Horn Hill". A slightly later charter, from 973, records the manor as Harawille. The Domesday Book of 1086 records the manor as Harwelle. Another 11th-century source records it as Harowell. One 13th-century document records it as Arewell. Other 13th- and 14th-century sources record it as Harewell.
