Is there an adjectival form for "good etiquette"?
According to OED, the only "valid" adjectival derivative of etiquette is...
etiquettical - relating to etiquette; observing or prescribed by etiquette
...for which the most recent of their six citations is...
2008 National Post (Canada) (Nexis) 10 May (Weekend section) 2
"None of this would have happened had he done the etiquettical thing"
There are several hundred instances of "etiquettical" in Google Books. Leafing through them I can't see any where the term is directly applied to a person, but the observing ... etiquette definition above certainly implies that in principle it could be thus used.
As to the alternative derivation etiquettal (which doesn't seem to feature in any authoritative dictionaries), I would simply note that there are only 15 legible instances in Google Books, all from the past few decades. In light of that I'd say it's just an erroneous form.
In practice it seems people don't actually apply etiquettical (or its bastard offspring etiquettal) to people, even if in principle they could). Probably the most common adjective (putting aside nitpicking over fine semantic distinctions) is OP's own courteous, but I think it's worth noting that manners shares with etiquette the fact that although it can be qualified both positively and negatively (good manners, bad manners), the default interpretation of the word is positive.
So although there are adjectival forms such as ill-mannered and well-mannered, we don't actually need to qualify the term to force the positive interpretation. Here's an instance in a letter from Byron (pub. 1844)...
I desire nothing better than to dine in company with such a mannered man every day in the week :
but of " his character" I know nothing personally; I can only speak to his manners, and these have my warmest approbation.
Though not used very often, in fact, very rarely, there does exist an adjective for "etiquette", as described here and here
etiquettal English[edit] Adjective[edit]
(rare) Of, or pertaining to, etiquette.
However, for all practical purposes, you're better off using terms like "well-mannered".
Check out the definition of the term from the Merriam-Webster link
well–mannered adjective
: having or displaying good manners : showing good taste : properly behaved : courteous, polite, well-bred
Also, take a look at usage of this term in some sentences, here, such as-
She is a very well-mannered and polite young woman who engages well with all and particularly contributed to great teamwork with her male classmates
I'm going to suggest proper. Though, it is usually used with a noun after.
Strictly following rules or conventions, especially in social behavior; seemly: a proper lady; a proper gentleman.
http://www.thefreedictionary.com/proper
There is also a loan phrase from French, comme il faut, which literally means 'as is necessary' and it can be used in the same sense of proper.
Correct in behaviour or etiquette: my friend is partial to cocaine—in every other way he is very proper and comme il faut
And there is decorous which is used for proper people who behaves with decorum.
Social decorum sets down appropriate social behavior and propriety, and is thus linked to notions of etiquette and manners.
Source: http://en.wikipedia.org/wiki/Decorum
characterized by dignified propriety in conduct, manners, appearance, character, etc.
Source:http://dictionary.reference.com/browse/decorous
The book "The Facts on File Guide to Good Writing" (By Martin H. Manser) explains the difference between decorous and decent and I wanted to share because it is related:
