The Collaborative International Dictionary of English v.0.48:

Lex \Lex\ (l[e^]ks), n.; pl. Leges (l[=e]"j[=e]z). [L. See
   Legal.]
   Law; as, lex talionis, the law of retaliation; lex terr[ae],
   the law of the land; lex fori, the law of the forum or court;
   lex loci, the law of the place; lex mercatoria, the law or
   custom of merchants.
   [1913 Webster]

The Free On-line Dictionary of Computing (19 January 2023):

Lex

   1.  A lexical analyser generator for Unix and its
   input language.  There is a GNU version called flex and a
   version written in, and outputting, SML/NJ called ML-lex.
   A version, by David Poole at Montana has been retargeted to
   Turbo Pascal, (ftp://iecc.com/pub/file/lyprg.zip).

   ["Lex - A Lexical Analyzer Generator", M.E. Lesk, CS TR 39,
   Bell Labs, Oct 1975].

   2.  The lexical specification
   language for COPS.

   ["Metalanguages of the Compiler Production System COPS",
   J. Borowiec, in GI Fachgesprach "Compiler-Compiler", ed
   W. Henhapl, Tech Hochs Darmstadt 1978, pp.122-159].

   (2000-11-15)