The Collaborative International Dictionary of English v.0.48:

Lancet \Lan"cet\, n. [F. lancette, dim. of lance lance. See
   Lance.]
   1. A surgical knife-like instrument of various forms,
      commonly sharp-pointed and two-edged, used in venesection,
      and in opening abscesses, etc.
      [1913 Webster]

   2. (Metal.) An iron bar used for tapping a melting furnace.
      --Knight.
      [1913 Webster]

   Lancet arch (Arch.), a pointed arch, of which the width, or
      span, is narrow compared with the height.

   Lancet architecture, a name given to a style of
      architecture, in which lancet arches are common; --
      peculiar to England and 13th century.
      [1913 Webster] lancetfish

WordNet (r) 3.0 (2006):

lancet
    n 1: an acutely pointed Gothic arch, like a lance [syn: lancet
         arch, lancet]
    2: a surgical knife with a pointed double-edged blade; used for
       punctures and small incisions [syn: lancet, lance]