The name which DB spells Austin(us) and Augustinus has been regarded as the Latin masculine name Augustinus and an Old French diminutive Austin (von Feilitzen 1937: 169), but the presence of that name in England in 1066 would be very surprising indeed.
Despite the prestige of the Roman missionary St Augustine of Canterbury (d. 604), his name seems not to have been adopted in England even by the clergy as a religious name, let alone by lay people. Not a single instance of the name has been traced in England between St Augustine and its supposed occurrence in DB (PASE: Augustine 1–2; Austin 1).
The presence of Austinus alongside the name Turstinus at a manor in Shropshire TRE encourages the idea that it might represent a Scandinavian name, since Turstinus is certainly derived ultimately from the name normalized in Old Norse as Thorsteinn, including as its second element steinn ‘stone’ (Fellows Jensen 1968: 351). Several of the names which DB spells with Au– represent Scandinavian names in Auð– (an element of obscure meaning) (Auduid for the name normalized as ON Auðviðr; Audulf for ON Auðulfr; and Augi for ON Auðgi). When such names were written in the twelfth century they had often lost the letter –ð– altogether. Austin, then, might represent the masculine Scandinavian name which would be normalized as Auðsteinn, though such a name seems not to be recorded in England (Björkman 1910: 22–4; Fellows Jensen 1968: 37–42, 342). It would have been rendered Augustinus by people in Norman England who wrongly equated it with the late Latin name.
Both Phillimore and Alecto follow the DB spellings and render the name Austin in Shropshire and Augustine in Staffordshire and Sussex.
von Feilitzen 1937: Olof von Feilitzen, The Pre-Conquest Personal Names of Domesday Book, Nomina Germanica 3 (Uppsala: Almqvist and Wiksells, 1937)
Fellows Jensen 1968: Gillian Fellows Jensen, Scandinavian Personal Names in Lincolnshire and Yorkshire (Copenhagen: I Kommission hos Akademisk Forlag, 1968)
Spellings in Domesday Book:
Forms in modern scholarship:
von Feilitzen head forms: