Use 'decorous' when describing behavior that fits well in formal or respectful social settings. The guests maintained a decorous silence as the ceremony proceeded.
Pro Tip 2/3
Cultural Expectations
What is considered 'decorous' can vary between cultures; be mindful of local customs. In Japan, a decorous greeting involves a bow rather than a handshake.
Pro Tip 3/3
Subtle Disapproval
'Decorous' sometimes implies restraint due to societal expectations, not personal choice. Although she was angry, her response was decorous and measured.