This list is far from comprehensive, but might be sufficient to get you started. All links are live as of 22 January 2024:
The obvious answer is the Oxford English Dictionary. Being a historical dictionary, it furnishes a record of the meanings of words over time, so consulting it liberally is advisable.
The specific book you are looking for is Kenneth C. Phillipps' Jane Austen's English. Here, for example, is part of his discussion of the word horrid:
Descriptive of the 'Gothic' romances, it retains a meaning nearer its etymology (Latin horridus 'prickly, rough, shaggy') of causing a bristling or shuddering with fear, and this meaning she endorses:
"...Midnight Bell, Orphan of the Rhine, and Horrid Mysteries. These will last us some time."
"Yes ... but are they all horrid, are you sure they are all horrid?"
(NA 40)
But when Isabella Thorpe refers to Sir Charles Grandison (NA 41), and her brother to Fanny Burney's Camilla (NA 49) as horrid, expressing thereby strong, though vague disapproval, their creator clearly does not approve of the extension of meaning.
Phillipps, K. C. Jane Austen's English. London: Andre Deutsch, 1970. Accessed at the Internet Archive. pp. 18–19, ellipses in original.
- R W Chapman has an essay on "Miss Austen's English" as an appendix to his edition of Sense and Sensibility. Here is a sample:
ascertain never means merely find out: it can be used with an impersonal subject: N A 67 Morland produced his watch, and ascertained the fact; 169 . . . the precious manuscript, for half a glance sufficed to ascertain written characters.
Chapman, R. W. "Miss Austen's English." Appendix to The Novels of Jane Austen, ed. R. W. Chapman. 3rd ed. London: OUP, 1933. Vol. I, pp. 388–421. Accessed at the Internet Archive. pp. 391–392, ellipses in original.
J. F. Burrows' Computation into Criticism: A Study of Jane Austen's Novels and an Experiment in Method (Oxford: Clarendon, 1987), also available at the indispensible Internet Archive, is a pioneering stylometric analysis of Austen's language.
There are of course dozens of studies of individual words. To take one instance, Janine Barchas's “Very Austen: Accounting for the Language of Emma”, published in Nineteenth-Century Literature, vol. 62, no. 3, 2007, pp. 303–38, and available on JSTOR, discusses Austen's use of "very" in Emma. The footnotes appurtenant thereto furnish many more references that you might find useful.
Good luck!