The Collaborative International Dictionary of English v.0.48:

Slow \Slow\ (sl[=o]), a. [Compar. Slower (sl[=o]"[~e]r);
   superl. Slowest.] [OE. slow, slaw, AS. sl[=a]w; akin to OS.
   sl[=e]u blunt, dull, D. sleeuw, slee, sour, OHG. sl[=e]o
   blunt, dull, Icel. sl[=o]r, sl[ae]r, Dan. sl["o]v, Sw.
   sl["o]. Cf. Sloe, and Sloth.]
   1. Moving a short space in a relatively long time; not swift;
      not quick in motion; not rapid; moderate; deliberate; as,
      a slow stream; a slow motion.
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   2. Not happening in a short time; gradual; late.
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            These changes in the heavens, though slow, produced
            Like change on sea and land, sidereal blast.
                                                  --Milton.
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   3. Not ready; not prompt or quick; dilatory; sluggish; as,
      slow of speech, and slow of tongue.
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            Fixed on defense, the Trojans are not slow
            To guard their shore from an expected foe. --Dryden.
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   4. Not hasty; not precipitate; acting with deliberation;
      tardy; inactive.
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            He that is slow to wrath is of great understanding.
                                                  --Prov. xiv.
                                                  29.
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   5. Behind in time; indicating a time earlier than the true
      time; as, the clock or watch is slow.
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   6. Not advancing or improving rapidly; as, the slow growth of
      arts and sciences.
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   7. Heavy in wit; not alert, prompt, or spirited; wearisome;
      dull. [Colloq.] --Dickens. Thackeray.
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   Note: Slow is often used in the formation of compounds for
         the most part self-explaining; as, slow-gaited,
         slow-paced, slow-sighted, slow-winged, and the like.
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   Slow coach, a slow person. See def.7, above. [Colloq.]

   Slow lemur, or Slow loris (Zool.), an East Indian
      nocturnal lemurine animal (Nycticebus tardigradus) about
      the size of a small cat; -- so called from its slow and
      deliberate movements. It has very large round eyes and is
      without a tail. Called also bashful Billy.

   Slow match. See under Match.
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   Syn: Dilatory; late; lingering; tardy; sluggish; dull;
        inactive.

   Usage: Slow, Tardy, Dilatory. Slow is the wider term,
          denoting either a want of rapid motion or inertness of
          intellect. Dilatory signifies a proneness to defer, a
          habit of delaying the performance of what we know must
          be done. Tardy denotes the habit of being behind hand;
          as, tardy in making up one's acounts.
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WordNet (r) 3.0 (2006):

slowest
    adv 1: most slowly