The Collaborative International Dictionary of English v.0.48:

Finder \Find"er\, n.
   1. One who, or that which, finds; specifically (Astron.), a
      small telescope of low power and large field of view,
      attached to a larger telescope, for the purpose of finding
      an object more readily, called also a finder telescope
      or finder scope.
      [1913 Webster +PJC]

   2. (Micros.) A slide ruled in squares, so as to assist in
      locating particular points in the field of vision.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

finder
    n 1: someone who comes upon something after searching
    2: someone who is the first to observe something [syn: finder,
       discoverer, spotter]
    3: optical device that helps a user to find the target of
       interest [syn: finder, viewfinder, view finder]

The Free On-line Dictionary of Computing (30 December 2018):

Finder

    The part of the Macintosh Operating
   System and GUI that simulates the desktop.  The
   multitasking version of Finder was called "MultiFinder"
   until multitasking was integrated into the core of the OS
   with the introduction of System 7.0 in 1990.

   (2005-03-18)