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

• stubborn
• stubbornly
• stubbornness
• Stubbs
• stubby
• stucco
• stuck
• stuck with
• stuck-up
• stud
• stud farm
• stud finder
• stud mare
• stud poker
• studbook
• studded
• studdingsail
• student
• student center
• student centre
• student lamp
• student lodging
• student nurse
• student residence
• student teacher