Definition of "pleonastic"

A second class of Subject Expressions in English are so-called pleonastic pronouns such as it and there in sentences like: (104) (a) It is raining/It is a long way to Dallas/Itʼs time to leave/It is obvious that youʼre right (104) (b) There must have been some mistake/There walked into the room the most beautiful woman I had ever encountered These Pronouns are called ‘pleonasticʼ (which means ‘redundantʼ) in traditional grammar because (in their ‘pleonasticʼ use, but not in other uses) they are felt to be (in some vague intuitive sense) ‘semantically emptyʼ, and thus cannot have their reference questioned (cf. ✽What is raining? ✽Where must have been some mistake?).

1988, Andrew Radford, chapter 6, in Transformational grammar: a first course, Cambridge, UK: Cambridge University Press, page 319

In these sentences finchè[sic] may be followed by a non which is called ‘pleonastic’ and does not negate the predicate in the subordinate clause: Ugo aspetta finchè non lo chiamano 'Ugo is waiting until they call him'. When the main clause is negative one must always use the pleonastic non after finchè in the subordinate clause: Ugo non si muove finchè non lo chiamano 'Ugo is not moving until they call him'.

1988 [Hutchinson Educational], Anna Laura Lepschy, Giulio C. Lepschy, The Italian Language Today, 2nd Edition, Reprinted 1992, Taylor & Francis (Routledge), page 107

Before undertaking to show the connection which this papyrus seems to establish between an apparently historical king of the IId dynasty and the hero of a romance of the XIXth (an interval of two or three thousand years), I will give an English version of Dr. Brugsch's German translation, condensing somewhat its more pleonastic passages, but preserving its genuine Egyptian features.

1869, J. P. Lesley, “Notes on Some of the Historical and Mythological Features of the D'Orbiney Papers”, in Proceedings of the American Philosophical Society, Volume 10: January 1865-December 1868, American Philosophical Society, page 543

A characteristic intension of a term unambiguously describes the extension of that term. But a characteristic intension of a term may be pleonastic, i.e., it may contain more properties than it is necessary to define the extension of that term. For instance, the intension of the term "square" consisting of the properties "planeness, quadrilaterality, rectangularity, equilaterality, being inscribable in a circle" would be pleonastic since it would include more properties than it is necessary to describe the extension of the term "square". […] The complete intension always is characteristic and pleonastic. It is the most pleonastic of all those intensions which are characteristic of a given set of objects.

1974, Olgierd Wojtasiewicz (translator), Kazimierz Ajdukiewicz, Pragmatic Logic, D. Reidel Publishing Company, PWN-Polish Scientific Publishers, page 44

To sum up, it may be said that the prediction of loss is borne out by the facts in Latvian and its dialects: the highly marked pleonastic morphology is no longer part of the system. […] However, within the Lithuanian dialect cluster, pleonastic morphology is still a long way from collapsing altogether.

2010, Thomas Stolz, “Pleonastic morphology dies hard”, in Franz Rainer, Wolfgang U. Dressler, Dieter Kastovsky, Hans Christian Luschützky, editors, Variation and Change in Morphology, page 241