A sharp two- edged surgical instrument, used in venesection and in opening abscesses, & c; a high and narrow window, pointed like a lancet. Lancet- arch, a narrow pointed Gothic arch.
- Nuttall's Standard dictionary of the English language. By Nuttall, P.Austin. Published 1914. (noun) (n.) (noun)
A sharply pointed surgeon's knife.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (noun) (n.) (noun)
A small, sharp, two- edged knife used by surgeons to open veins, tumours, & c.
- Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874. (noun) (n.) (noun)
A surgical instrument used for opening veins, etc.: a high and narrow window, pointed like a lance.
- The american dictionary of the english language. By Daniel Lyons. Published 1899. (noun) (n.) (noun)
A surgical instrument for letting blood, & c.
- The Clarendon dictionary. By William Hand Browne, Samuel Stehman Haldeman. Published 1894. (noun) (n.) (noun)

Usage examples:

Lord, Lord, had I but a lancet and a purge for the spirit as you for the flesh, there would be not only no sin but no souls left in the Colony!
- The Heart's Highway A Romance of Virginia in the Seventeeth Century by Mary E. Wilkins
The London Lancet said in its obituary: By the death of Sir Dominic Corrigan, the medical profession loses one of its most conspicuous members, the University at Edinburgh one of its most illustrious graduates, and the Irish race one of its finest specimens.
- Makers of Modern Medicine by James J. Walsh
Enormous narrow lancet windows showed above the line of chapels, springing perhaps forty feet from the ground, and rising to a line immediately below the roof.
- Dawn of All by Robert Hugh Benson