The Only Use of

lexicon
in
The Mill on the Floss

But the revolutions round the table became more and more irregular in their sweep, till at last reaching Mr. Stelling's reading stand, they sent it thundering down with its heavy lexicons to the floor.†
Chpt 2.1

Definitions:

(1) (lexicon)
a list of words used in a particular subject area or known by an individual
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

More formally, lexicon may refer to a dictionary that attempts to accompany each head word with all the forms of the word used in a language. For example, a dictionary would usually list reading and reads with read, but a lexicon would also list readable, readability, and reader.