The Collaborative International Dictionary of English v.0.48:

Closemouthed \Close"mouthed`\, a.
   Cautious in speaking; secret; wary; uncommunicative.
   [1913 Webster]

WordNet (r) 3.0 (2006):

closemouthed
    adj 1: inclined to secrecy or reticence about divulging
           information; "although they knew her whereabouts her
           friends kept close about it" [syn: close,
           closelipped, closemouthed, secretive,
           tightlipped]