1.Definition: cool and formal in manner

Related Adjective(s):reticent, unemotional

2.Definition: marked by avoidance of extravagance or extremes

"Restrained in his response"

Related Adjective(s):moderate

3.Definition: not showy or obtrusive

Related Adjective(s):quiet

4.Definition: prudent

Related Adjective(s):guarded

5.Definition: under restraint