inhibited

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adjective

1. Tending to keep one's thoughts and emotions to oneself: controlled, noncommittal, reserved, restrained, self-controlled, self-restrained. See restraint/unrestraint.
2. Deficient in or lacking sexual desire: ardorless, cold, frigid, passionless, unresponsive. See sex/asexual.

Definition: very shy
Antonyms: aggressive, bold, extrovert, forward, immodest, self-confident, uninhibited

The adjective has one meaning:

Meaning #1: held back or restrained or prevented
  Antonym: uninhibited (meaning #1)