The Collaborative International Dictionary of English v.0.48:

Secretive \Se*cret"ive\, a.
   Tending to secrete, or to keep secret or private; as, a
   secretive disposition.
   [1913 Webster]

WordNet (r) 3.0 (2006):

secretive
    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]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "secretive":
   close, closemouthed, dark, discreet, disinclined to communicate,
   evasive, excretory, lachrymal, lachrymose, lacrimatory,
   lactational, lacteal, lacteous, meaningless, mum, reserved,
   reticent, rheumy, salivant, salivary, salivous, secret,
   secretional, secretory, seminal, serous, shifty, sialagogic,
   silent, spermatic, taciturn, tight-lipped, uncommunicative,
   unconversable, unsociable, watering, watery