[f. as prec. + -ING1.] The action of the verb THICKEN; the process of making or becoming thick or thicker; concr. the result of this action or process; a thickened substance or part.
1580. Hollyband, Treas. Fr. Tong, Espessissement, a thickening.
1603. Holland, Plutarch’s Mor., 998. Mists, fogs, and clouds are no congealations, but onely gatherings, and thickenings of a moist and vapourous aire.
1822. J. Parkinson, Outl. Oryctol., 159. A subglobose univalve; the opening longer than wide; no thickening of the left lip.
1893. Tuckey, trans. Hatschek’s Amphioxus, 154. He was misled by a thickening of the alimentary canal in front of the gland.
1899. Allbutt’s Syst. Med., VIII. 51. Eczema of the palms very frequently leads … to great thickening of the epidermis.
c. 1900. Beeton’s Everyday Cookery Bk., 209/2. By the addition of various store sauces, thickening and flavouring, good stock may be converted into good gravies.
b. A substance used to thicken something; spec. in Dyeing. = THICKENER.
1839. Ure, Dict. Arts, etc., 222. Several circumstances may require the consistence of the thickening to be varied.
1874. W. Crookes, Dyeing & Calico-print., ii. 17. Only two mineral thickenings are at present employed, namely, kaolin and pipe-clay.
c. Foundry = THICKNESS 8.
1872. Ellacombe, Bells of Ch., i. 200. When thoroughly dried, the outer mould is removed, and the thickening (the fac-simile of the bell) destroyed.
d. Bot. Thickening layer, mass, ring (Ger. verdickungsring): see quots.
1875. Bennett & Dyer, trans. Sachs’s Bot., 27. A wider cavity, which is bounded on the sides by the narrow part of the thickening-masses, on the outside by the primary cell-wall. Ibid., 108. Generating ring of tissue, corresponding to Sanio’s thickening ring.
1900. B. D. Jackson, Gloss. Bot. Terms, 270/2. Thickening Layer, an apparent layer of cellulose on the inner face of a cell-wall; Thickening Ring, Sanio’s term for a ring of meristem in which the first fibro-vascular bundles originate.
