The Collaborative International Dictionary of English v.0.48:

Resolver \Re*solv"er\ (r?-z?lv"?r), n.
   1. That which decomposes, or dissolves. --Boyle.
      [1913 Webster]

   2. That which clears up and removes difficulties, and makes
      the mind certain or determined. --Bp. Burnet.
      [1913 Webster]

   3. One who resolves, or formal a firm purpose.
      [1913 Webster]

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

resolver

    The TCP/IP protocol library software that
   formats requests to be sent to the Domain Name Server for
   hostname to IP address conversion.

   (1995-03-28)