The Jargon File (version 4.4.7, 29 Dec 2003):

nanobot
 /nan'oh?bot/, n.

    A robot of microscopic proportions, presumably built by means of 
    nanotechnology. As yet, only used informally (and speculatively!). Also
    called a nanoagent.


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

nanobot

    /nan"oh-bot/ A robot of microscopic proportions,
   presumably built by means of nanotechnology.  As yet, only
   used informally (and speculatively!).  Also called a
   "nanoagent".

   [Jargon File]

   (1999-07-19)