The Collaborative International Dictionary of English v.0.48:

Cretinous \Cre"tin*ous\ (-[u^]s), a.
   Having the characteristics of a cretin. "Cretinous
   stupefaction." --Ruskin.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cretinous
    adj 1: afflicted with cretinism

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

cretinous
 /kret'n?@s/, /kreet?n?@s/, adj.

    Wrong; stupid; non-functional; very poorly designed. Also used pejoratively
    of people. See dread high-bit disease for an example. Approximate
    synonyms: bletcherous, bagbiting, losing, brain-damaged.