The Collaborative International Dictionary of English v.0.48:

So-called \So"-called`\, a.
   So named; called by such a name (but perhaps called thus with
   doubtful propriety).
   [1913 Webster]

WordNet (r) 3.0 (2006):

so-called
    adj 1: doubtful or suspect; "these so-called experts are no
           help" [syn: alleged(a), so-called, supposed]