a. Chiefly scientific and technical. [f. late L. synchronus, a Gr. σύγχρονος, f. σύν SYN- + χρόνος time: see -OUS.]
1. Existing or happening at the same time; coincident in time; belonging to the same period, or occurring at the same moment, of time; contemporary; simultaneous. Const. with.
1669. Gale, Crt. Gentiles, I. II. v. 56. Hercules, the Tyrian Commander; whom some make synchronous with Moses.
1772. Nugent, Hist. Fr. Gerund, I. 217. It is affirmed by a coetaneous, syncronous, and faith-worthy author.
1833. Lyell, Princ. Geol., III. 42. Formations, which, although dissimilar both in organic and mineral characters, were of synchronous origin.
1872. Nicholson, Palæont., 19. Synchronous deposits necessarily contain wholly different fossils, if one has been deposited by fresh water, and the other has been laid down in the sea.
1878. Bates, Centr. Amer., vi. 78. The rainy season on the coasts is not synchronous with that of the uplands.
b. transf. Relating to or treating of different events or things belonging to the same time or period; involving or indicating contemporaneous or simultaneous occurrence.
1823. Thomasina Ross, Bouterwek’s Hist. Sp. Lit., I. 499. A synchronous account of all the remarkable productions of the polite literature of Spain.
1843. Civil Eng. & Arch. Jrnl., VI. 159/2. Where is the line to be drawn by which different styles ought to have been set apart as worthy to afford a new starting point for synchronous treatment?
1882–3. Schaff’s Encycl. Relig. Knowl., 1249. The synchronous history of the divided kingdoms of Israel and Judah.
c. Synchronous curve (Geom.), a curve which is the locus of the points reached at any instant by a number of particles descending from the same point down a family of curves under the action of gravity.
1867. Brande & Cox, Dict. Sci., etc., III. 685.
2. Recurring at the same successive instants of time; keeping time with; going on at the same rate and exactly together; having coincident periods, as two sets of vibrations or the like.
1677. F. North, Philos. Ess. Mus., 20. The synchronous motion of the pulses at the mouth of the Pipe with the vibrations of the included Air promote the Sound of the Pipe.
1733. Arbuthnot, Ess. Air, ii. 29. The Variations of the Gravity of the Air keep both the Solids and the Fluids in an oscillatory Motion, synchronous, and proportional to their Changes.
1786. J. Pearson, in Med. Commun., II. 93. Pulsation…, synchronous with that of the radial artery.
1866. Dk. Argyll, Reign of Law, iii. (1867), 173. The beats of a bird’s two wings are always exactly synchronous.
1871. Tyndall, Fragm. Sci. (1879), I. xiv. 391. Affected by those undulations which are synchronous with their own periods of vibration.
1899. Allbutt’s Syst. Med., VIII. 42. The spasms of the face and those of the palate were not synchronous.
b. Electr. applied to alternating currents having coincident periods; also to a machine or motor working in time with the alternations of current.
1901. A. Russell, in Electr. Rev., 19 July, 88/1. The Power Factor of a Synchronous Motor.
¶ erron. Of uniform velocity.
1785. Reid, Intell. Powers, II. iv. 253. That relation of synchronous vibrations which produces harmony.
