"relating to the vocabulary of a language," 1833, from a Latinized form of Greek lexikos "pertaining to words" (see lexicon) + -al (1). Related: Lexically.
Entries linking to lexical
lexicon n.
c. 1600, "a dictionary, a word-book," from French lexicon or directly from Modern Latin lexicon, from Greek lexikon (biblion) "word (book)," from neuter of lexikos "pertaining to words," from lexis "a word, a phrase; reason; way of speech, diction, style," from legein "to say" (from PIE root *leg- (1) "to collect, gather," with derivatives meaning "to speak (to 'pick out words')").
Especially of dictionaries of Greek, Syriac, Hebrew, or Arabic, because these typically were written in Latin, and in Modern Latin lexicon (not dictionarius) was the preferred name for a word-book. The modern sense of "vocabulary proper to some sphere of activity" (1640s) is a figurative extension.
-al 1
suffix forming adjectives from nouns or other adjectives, "of, like, related to, pertaining to," Middle English -al, -el, from French or directly from Latin -alis (see -al (2)).