Sentence:  Whenever Root would put his elbows on the table or clatter his dishes or commit any other breach of <WSD>etiquette</WSD>, the Professor would gently correct him. 
Meaning of the word marked with <WSD> tags:  The forms required by a good upbringing, or prescribed by authority, to be observed in social or official life; observance of the proprieties of rank and occasion; conventional decorum; ceremonial code of polite society.