A Dictionary of Linguistics and Phonetics David Crystal

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grammar. The mental lexicon is the stored mental representation of what we
know about the lexical items in our language.
lexicon optimization An algorithm in optimality theory which evaluates
candidate input forms with respect to the actual output. A series of tableaux
is examined, and the input–output pair receiving the fewest constraint violations
is chosen as the optimal input.
lexicostatistics (n.) A technique used in glottochronology with which one
attempts to make quantitative comparisons between the rates of change within
sets of lexical items in hypothetically related languages, and thus to deduce
the distance in time since the languages separated. Other types of lexical comparison
(e.g. to determine the mutual intelligibility of languages) may also be
referred to by this label.
lexis (n.) A term used in linguistics to refer to the vocabulary of a language,
and used adjectivally in a variety of technical phrases. A unit of vocabulary is
generally referred to as a lexical item, or lexeme. A complete inventory of the
lexical items of a language constitutes that language’s dictionary, or lexicon –
a term particularly used in generative grammar: items are listed ‘in the lexicon’
as a set of lexical entries. The way lexical items are organized in a language
is the lexical structure or lexical system. A group of items used to identify the
network of contrasts in a specific semantic or lexical field (e.g. cooking, colour)
may also be called a ‘lexical system’. Specific groups of items, sharing certain
formal or semantic features, are known as lexical sets. The absence of a lexeme
at a specific structural place in a language’s lexical field is called a lexical gap
(e.g. brother v. sister, son v. daughter, etc., but no separate lexemes for ‘male’ v.
‘female’ cousin). In comparing languages, it may be said that one language may
lexicalize a contrast, whereas another may not – that is, the contrast is identified
using lexemes, as in the many terms for the English lexeme ‘hole’ available in
some Australian Aboriginal languages. Lexis may be seen in contrast with grammar,
as in the distinction between ‘grammatical words’ and lexical words:
the former refers to words whose sole function is to signal grammatical relationships
(a role which is claimed for such words as of, to and the in English); the
latter refers to words which have lexical meaning, i.e. they have semantic content.
Examples include lexical verbs (v. auxiliary verbs) and lexical noun phrases
(v. non-lexical NPs, such as PRO). A similar contrast distinguishes lexical
morphology from derivational morphology. Hallidayan linguistics makes a
theoretical distinction between grammar and lexis, seen as two subdivisions
within linguistic form: lexis here is studied with reference to such formal
concepts as collocation, and not in semantic terms. The mutual restriction
governing the co-occurrence of sets of lexical items is known as lexical
selection (e.g. animate nouns being compatible with animate verbs). Lexical
density is a measure of the difficulty of a text, using the ratio of the number of
different words (the ‘word types’) to the total number of words (the ‘word
tokens’): the ‘type/token ratio’.
In generative grammar, the insertion of particular lexemes at particular places
in grammatical structures is carried out by a process of lexical substitution
or lexical transformation, using lexical insertion rules. Lexical redundancy rules