The word τερθρεία, which L. and S.8 derived (following Moeris) from τερατεία and translated ‘the use of claptraps’, is perhaps best known from its occurrence in Isocrates (Helen, § 4), but the new edition has spread the net more widely, citing Philo, Philodemus, Proclus, Galen, Dion. Hal., and giving its meaning as ‘the use of extreme subtlety, hair-splitting, formal pedantry’. This agrees better with the gloss / κενοσπονδία attributed to Orus of Miletus in Et. Mag. 753. 4. Aristotle, Demosthenes, and Plutarch each use τερθρεύομαι once. In the Helen Isocrates, condemning the futile ingenuity of the Sophists in writing encomia on such unworthy objects as salt and humble-bees, holds that such tours de force are immoral, as (i) tending to deceive, (ii) representing a literary form of the vice περιεργία. Τερθρεία, then, should take its place, as a recognized term for the idle over-elaboration of a banausic theme, in the vocabulary of Greek literary criticism. It does not, however, appear in Rhys Roberts's ‘Glossary of Greek Rhetoric’ appended to his edition of D.H.'s On Literary Composition. No doubt this is because τερθρεία does not occur in this or any other of D.H.'s Scripta Rhetorica. But D.H. himself uses the word in Antiq. Rom. (ii. 19). Similarly J. F. Lockwood does not discuss the term in his lists in C.Q. xxxi and xxxii, where he collects words which are used metaphorically by D.H. in literary criticism. The metaphor in τερθρεία is certainly not obvious; but the literary sense must have involved some transference of meaning, for it is not to be expected that the word τερθρεία sprang, in full panoply of critical significance, from the brain of the Muse of Rhetoric; and it is part of the purpose of this paper to point the way to an explanation, or at least to set forth some known facts about the word and its possible congeners.