WordWeb Online

1. Cool and formal in manner
   - reticent, unemotional
    
2. Under restraint
    
3. Marked by avoidance of extravagance or extremes
   "restrained in his response"
   - moderate
    
4. Not showy or obtrusive
   - quiet
    
5. Prudent
   - guarded

1. Keep under control; keep in check
   - keep, keep back, hold back
    
2. Place limits on (extent or access)
   - restrict, trammel, limit, bound, confine, throttle
    
3. To close within bounds, limit or hold back from movement
   - confine, hold
    
4. Hold back
   - encumber, cumber [archaic], constrain
    
5. To compel or deter by or as if by threats
   - intimidate

See also: cautious, close, controlled, inhibited, low-key, low-keyed, reserved, restrainer, restraint, subdued, temperate, undemonstrative, unexpansive, unostentatious, unpretending, unpretentious

Type of: bottle up, check, contain, control, curb, disable, discourage, disenable, hold, hold in, incapacitate, inhibit, moderate, suppress

Antonym: unrestrained