Reserved (-zrvd), a.
1. Kept for future or special use, or for an exigency; as, reserved troops; a reserved seat in a theater.
2. Restrained from freedom in words or actions; backward, or cautious, in communicating one's thoughts and feelings; not free or frank. To all obliging, yet reserved to all. Walsh. Nothing reserved or sullen was to see. Dryden. -- Re*serv"ed*ly (r, adv. -- Re*serv"ed*ness, n.
Shades of meaning
Fernald has no entry of its own for reserved; he lists it under taciturn.
Where he writes about it:
Reserved suggests more of method and intention than taciturn, applying often to some special time or topic; one who is communicative regarding all else may be reserved about his business. — from taciturn
Reserved is thus closely equivalent to uncommunicative, but is a somewhat stronger word, often suggesting pride or haughtiness, as when we say one is reserved toward inferiors. — from taciturn