[ad. L. apertūra, f. apert- ppl. stem of aperīre to open: see -URE.]
† 1. The process of opening. Obs.
1669. Holder, Elem. Speech, 29 (J.). From an Appulse to no Appulse (or an Apperture) is easier … than from one Appulse to another.
1686. Goad, Celest. Bodies, I. vi. 21. The aperture and explication of the willing Flower.
1708. Phil. Trans., XXVI. 170. His Brother … desired an Eminent Surgeon … to open him; but as the Aperture was to be perform’d gratis, he put it off.
† 2. The opening up of what is involved, intricate, restricted. Obs. rare.
1649. Jer. Taylor, Gt. Exemp., Add. v. § 4. The apertures and permissions of marriage have such restraints of modesty and prudence, that [etc.]. Ibid. (1660), Worthy Commun., Introd. 8. The aperture and dissolution of distinctions.
3. An opening, an open space between portions of solid matter; a gap, cleft, chasm or hole; the mouth of the shell of a mollusk.
1665. Glanvill, Sceps. Sci., vi. 26. If memory be made by the easy motion of the Spirits through the open passages, images, without doubt, pass through the same apertures.
1696. Whiston, Th. Earth, IV. (1722), 409. So much Water was run down … as the Apertures could receive.
1794. Sullivan, View Nat., II. 88. The internal structure … may be compared to a spunge, though the apertures cannot in general be perceived.
1856. Woodward, Fossil Shells, 44. The thickening and contraction of the aperture in the univalves.
4. Opt. The space through which light passes in any optical instrument (though there is no material opening). Also attrib.
1664. Phil. Trans., I. 19. I saw … with one Aperture of my glass more than 40 or 50.
1751. Chambers, Cycl., s.v., The focal distances of the eye-glasses are to be proportional to the Apertures.
1879. Lockyer, Elem. Astron., vi. 218. The aperture of the object-glass, that is to say, its diameter.
1879. H. Grubb, in Proc. R. Dubl. Soc., 181. That roundness and relief that is admired so much in photographs taken with large aperture lenses.
5. ‘In some Writers of Geometry, the Inclination, or Leaning of one Right-line towards another, which meet in a point and make an Angle.’ Phillips, 1706.
So in Chambers, 1751; Hutton, 1796.
