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▪ I. dyad|ˈdaɪæd|
Also 7 diad.
[ad. L. dyas, dyad-, a. Gr. δυάς, δυάδ-, the number two.]
1. The number two; a group of two; a couple. Cf. duad 1.
1675R. Burthogge Causa Dei 244 Now a Monad and a Diad, or One and Two, makes Three. 1678Cudworth Intell. Syst. 372 The Writer..doth affirm Pythagoras to have asserted Two Substantial Principles Self-existent, a Monad and a Dyad. 1809W. Irving Knickerb. (1849) 37 Pythagoras likewise inculcated the famous numerical system of the monad, dyad, and triad. 1885F. Hall in Ballantyne's Sánkhya Aphorisms 224 The gross product of Nature, viz., the great elements and the dyad of bodies.
2. In specific uses:
a. Chem. An atom, radical, or element that has the combining power of two units, i.e. of two atoms of hydrogen.
1865Reader 1 Apr. 372/2 Each of these atoms combines usually with three monads, or with one dyad and one monad. 1873Fownes' Chem. (ed. 11) 250 Sulphur, selenium, and tellurium, are usually regarded as dyads.
b. Biol. A secondary unit of organization consisting of an aggregate of monads. Hence dyaddeme.
1883[see deme].
c. Pros. A group of two lines having different rhythms.
1885B. L. Gildersleeve Pindar p. liii, Dyads and triads there are in Pindar, but they do not disturb the rhythmical working of the odes.
d. Math. An operator ab so defined that F. (ab) = (F.a)b for all F, where a and b are vectors and F is any linear vector function.
1884J. W. Gibbs Coll. Wks. (1928) II. ii. iii. 53 An expression of the form αλ or βµ will be called a dyad. 1933H. B. Phillips Vector Anal. x. 217 A linear equation satisfied by dyads will remain valid if each dyad is replaced by the dot or cross product of its two vectors. 1969Ll. G. Chambers Course Vector Anal. vi. 181 Consider now the dyad, or indefinite product of two vectors a and b, ab... This has the properties that (ab). F = a(b. F) and F. (ab) = (F. a)b.
3. attrib. or as adj. = dyadic.
1869Roscoe Elem. Chem. 266 Copper is a dyad element. 1881Athenæum 26 Mar. 433/1 He has also prepared the hydrate and oxalate of the dyad radical (C2H2Hg3O2).
Add:[2.] e. Anat. A structure found in vertebrate cardiac muscle and some insect muscle, consisting of a transverse tubule in contact with a terminal cisterna of the sarcoplasmic reticulum.
1957Porter & Palade in Jrnl. Biophysical & Biochem. Cytol. III. 286 Within the area enclosed by the arms of the U there may be an additional circular or oval profile which in some instances is continuous with the inner surface of the U-shaped element... This unit of two components will be referred to as a dyad. 1964Jrnl. Cell Biol. XXII. 694/1 In cardiac muscle and in certain insect muscles the homologue of the triad is to be found in the dyad. 1984J. F. Lamb et al. Essent. Physiol. (ed. 2) iii. 59 The T system opens to the extracellular space and is related to the SR [sc. sarcoplasmic reticulum] via a series of flattened membranous sacs (dyads).
▪ II. dyad, dyaf, dyaþ
ME. (Kentish) forms of dead, deaf, death n. |