tight·lipped also tight-lipped 
(tītlĭpt)
(tītlĭpt)adj.
1. Having the lips pressed together: a tightlipped smile.
2. Reluctant to speak; close-mouthed. See Synonyms at laconic.
3. Characterized by restraint or reserve in expression: The politician gave tightlipped responses to questions about the incident.
tightlippedness n.