The Collaborative International Dictionary of English v.0.48:

Certify \Cer"ti*fy\, v. t. [imp. & p. p. Certified; p. pr. &
   vb. n. Certifying.] [F. certifier, LL. certificare; L.
   certus certain + facere to make. See Certain, and cf.
   Certificate, v. t.]
   1. To give cetain information to; to assure; to make certain.
      [1913 Webster]

            We certify the king, that . . . thou shalt have no
            portion on this side the river.       --Ezra iv. 16.
      [1913 Webster]

   2. To give certain information of; to make certain, as a
      fact; to verify. --Hammond.
      [1913 Webster]

            The industry of science at once certifies and
            greatly extends our knowledge of the vastness of the
            creation.                             --I. Taylor.
      [1913 Webster]

   3. To testify to in writing; to make a declaration
      concerning, in writing, under hand, or hand and seal.
      [1913 Webster]

            The judges shall certify their opinion to the
            chancellor, and upon such certificate the decree is
            usually founded.                      --Blackstone.
      [1913 Webster]

   Certified check, A bank check, the validity of which is
      certified by the bank on which it is drawn.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

certified \certified\ adj.
   1. endorsed authoritatively as having met certain
      requirements; guranteed; as, certified milk; certified
      mail; a certified check. Opposite of uncertified.
      [Narrower terms: certificated, credentialed, documented;
      guaranteed] See also certifiable.
      [WordNet 1.5]

   2. legally insane according to clinical criteria.

   Syn: certifiable.
        [WordNet 1.5 +PJC]

   3. holding appropriate documentation and officially on record
      as qualified to perform a specified function or practice a
      specified skill.

   Syn: qualified.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

certified
    adj 1: endorsed authoritatively as having met certain
           requirements; "a certified public accountant" [ant:
           uncertified]
    2: fit to be certified as insane (and treated accordingly) [syn:
       certifiable, certified]
    3: holding appropriate documentation and officially on record as
       qualified to perform a specified function or practice a
       specified skill; "a registered pharmacist"; "a registered
       hospital" [syn: certified, qualified]