reticent (adj.)

• aloof
• backward
• bashful
• blank
• chilly
• close
• closemouthed
• cold
• constrained
• cool
• detached
• discreet
• distant
• expressionless
• forbidding
• frigid
• frosty
• guarded
• icy
• impassive
• impersonal
• inaccessible
• introverted
• modest
• offish
• quiet
• remote
• removed
• repressed
• reserved
• restrained
• retiring
• shrinking
• shy
• silent
• standoffish
• subdued
• suppressed
• taciturn
• timid
• unapproachable
• uncommunicative
• uncongenial
• undemonstrative
• unexpansive
• unresponsive
• withdrawn