Decorous comes from the Latin decorus ("seemly, fitting, proper, becoming"), which itself stems from decor ("beauty, grace, ornament"), linking it to words like decorate and decent.  Its root is the Proto-Indo-European dek- meaning "to take, accept," with the sense of adding grace, leading to terms for appropriateness and adornment.  Decorum also comes from the Latin decorus and means "behavior in keeping with good taste and propriety, etiquette". 

The earliest known use of the adjective decorous in English, according to the Oxford English Dictionary (OED), is from the writing of Henry More, a philosopher, poet, and theologian in 1664.  A slightly older sense of "decorous," meaning "fitting, appropriate," is now obsolete. The modern meaning, "characterized by or exhibiting decorum; proper," also dates from the mid-17th century.  According to the OED, the noun "decorum", meaning "dignified propriety; appropriate and proper behavior or appearance", first appeared in English in the mid-1500s, with the earliest known evidence coming from the writings of Roger Ascham, a royal tutor, before 1568, initially referring to literary appropriateness and later evolving to mean polite behavior. 

Examples of "decorous" used in a sentence: 
"Yates draws a decorous curtain around the rest of the scene." 
"Among the criers were some of the least decorous people in the country."
"In these coffee-houses, however, there generally prevails a very decorous stillness and silence." 
"The tone was decorous and reserved, a moving elegy delivered by someone who didn't know the deceased very well." 
"Without Stevenson, Sterne would probably have been a more decorous parish priest, but he would probably never have written Tristram Shandy or left any other memorial of his singular genius." 

Examples of "decorum" used in a sentence: 
"There was decorum in the countenance he wore." 
"We trust he will show the proper decorum for the occasion." 
"Your sense of ethics and social decorum is also strong as you strive to be your best.
"She accepted his report, not without obvious sadness but with business-like decorum and no sign of tears." 
"The boy had a wild streak that overcame his sense of decorum too often and landed him in duels every other day. 

Just the facts:

DECOROUS Definition & Meaning - Merriam-Webster

DECOROUS Synonyms: 86 Similar and Opposite Words | Merriam-Webster Thesaurus

While commenting on fabulous @Krista story Learned To Lie, I am always filled with decorous behavior. 

On 12/24/2025 at 9:34 AM, sandrewn said:

Merry Christmas!

(You're difficult to track down )