The Collaborative International Dictionary of English v.0.48:

Infamous \In"fa*mous\, a. [Pref. in- not + famous: cf. L.
   infamis. See Infamy.]
   [1913 Webster]
   1. Of very bad report; having a reputation of the worst kind;
      held in abhorrence; guilty of something that exposes to
      infamy; base; notoriously vile; detestable; as, an
      infamous traitor; an infamous perjurer.
      [1913 Webster]

            False errant knight, infamous, and forsworn.
                                                  --Spenser.
      [1913 Webster]

   2. Causing or producing infamy; deserving detestation;
      scandalous to the last degree; as, an infamous act;
      infamous vices; infamous corruption. --Macaulay.
      [1913 Webster]

   3. (Law) Branded with infamy by conviction of a crime; as, at
      common law, an infamous person can not be a witness.
      [1913 Webster]

   4. Having a bad name as being the place where an odious crime
      was committed, or as being associated with something
      detestable; hence, unlucky; perilous; dangerous. "Infamous
      woods." --P. Fletcher.
      [1913 Webster]

            Infamous hills, and sandy perilous wilds. --Milton.
      [1913 Webster]

            The piny shade
            More infamous by cursed Lycaon made.  --Dryden.

   Syn: Detestable; odious; scandalous; disgraceful; base; vile;
        shameful; ignominious.
        [1913 Webster]

WordNet (r) 3.0 (2006):

infamous
    adj 1: known widely and usually unfavorably; "a notorious
           gangster"; "the tenderloin district was notorious for
           vice"; "the infamous Benedict Arnold"; [syn: ill-famed,
           infamous, notorious]