1. In architecture, each of the small, rectangular blocks -- think of a row of teeth -- under the bed-molding of the cornice in the Ionic, Corinthian, Composite, and sometimes Doric, designs. In woodworking, smaller in scale, but with a similar location, just below the cornice. In the 18th-century, from Greek, Roman and Renaissance sources, Robert Adam (1728-1792), the Scottish architect and furniture designer, introduces over 100 ornaments, including the dentil, to furniture design. However, Charles Hayward (read more here) claims that dentils are a feature of Jacobean design, which makes dentils in use in Britain between 1603 and 1660.
2. In Corinthian architecture, a cog or toothed member, such as a rectangular supporting block commonly used in the bed mold of the entablature. Each cog or tooth is called a dentil.
3. A small rectangular block, forming one of a series closely set in a row, generally between two mouldings, and intended for ornamental effect by alternation of light, shade, and are found under the corona of an Ionic or Corinthian cornice. One of the earliest examples is in the cornice of the caryatid porch of the Erechtheum, Athens; another is that of the Choragic Monument of Lysicrates, while in Roman Ionic and even Roman Doric buildings it is a very common feature. In the Roman Corinthian, also, there is a row of dentils between two mouldings under the modulions. The proportions of classic dentils vary considerably ; in some of the best examples the width and projection are each equal to two thirds the height, and the inter-dentil or space is one third the height ; which approximates to one sixth the lower diameter of the column. (See image of page below on left.)
Source: Russell Sturgis, A Dictionary of Architecture and Building: Biographical, Historical, and ... 1901, volume 1
1663 Balthazar Gerbier, Counsel and Advise to all Builders; For the Choice of their Surveyours, Clarks of their Works, Bricklayers, Masons, Carpenters, and other Workmen therein concerned. As also, In respect of their Works, Materials and Rates thereof. Together with several Epistles to Eminent Persons, who may be Concerned in Building (London 1663) page 71
The Dentiles at three pence per foot.
Click on this link for a pdf, "modernized" version of this 17th-century book: http://archiv.ub.uni-heidelberg.de/artdok/volltexte/2008/546/pdf/Davis_Fontes8.pdf It is searchable, and "dentil" is mentioned several times.
On the left is an oak chest, dated 1680, -- in the George Dudley Seymour furniture collection-- with carved dentils. Seymour is a noted 19th-century Connecticut-based furniture collector. Where was this 17th-century chest made? But another question is answered: how do we know that Charles Hayward is correct when he claims that dentils were part of furniture construction during the Jacobean period, i.e., from 1603 to 1690?
Source: Wallace Nutting Furniture Treasury New York: Macmillan, 1928; Newton C. Brainard, George Dudley Seymour's Furniture Collection in the Connecticut Historical Society. Hartford; Connecticut Historical Society: 1958.
1812-1816 James Smith Panorama Science and Art volume 1, page 180
Under the modillions is placed an ovolo, and then a fillet and the dentil face, which is often left uncut in exterior work.
1823 P. Nicholson Practical Builder. 474
The dentil-bands should remain uncut.
1849 Edward Augustus Freeman, History of Architecture London: Masters, 1849, page 113
The dentils introduced just under the cornice, if not rich in themselves, are a great source of richness, by reason of the great scope they give for varieties of light and shade.
1865 J. G. Nichols Heraldry and Genealogy. July 254
The classical dentil moulding.
1959 Charles H. Hayward, English Period Furniture New York: Van Nostrand, 1959 and later
The case of Robert Adam as a designer of furniture is in a rather different category. Adam was an architect, not a practical cabinet maker, and he designed his furniture specially to suit the houses he built. It was natural, then, that his furniture should show more of a definite break from tradition, because he was not fettered by years of training in a certain established school (with whatever advantages and disadvantages that carries with it). At the same time, the fact that he became an extremely successful architect with a large clientele made it inevitable that he should attract the attention of many cabinet makers, who would make furniture which was either a copy of pure Adam work or was just founded upon it. Thus, except for certain authentic specimens, one cannot hope to do more than classify a piece as being in the style of Adam.
Both the text and the illustrations come from Charles H. Hayward's English Period Furniture
Sources: Walter E. Durbahn and J. Ralph Dalzell, Dictionary of Carpentry Terms CHICAGO:AMERICAN TECHNICAL SOCIETY, 1947 (Read more about Walt Durbahn here ); , "A Glossary of Robert Adam's Neo-Classical Ornament", Architectural History24 1981, pp. 59-82; this source includes excellent black-and-white illustrations.