What is a "Dublin Castle Knight"?

Question

I was reading Surtees' Young Tom Hall the other day, and came across this...

Sir Thomas, whose father had been a great army tailor, was a Dublin Castle knight, but, like all truly great men, condescending withal - and no feast or fete, or wedding, or christening, in Fleecyborough, or within a radius of three miles, was considered perfect without Sir Thomas Thimbleton of Thimbleton Park (so he called his villa and twenty acres of land).

Does anyone know what a Dublin Castle knight is? It doesn't sound terribly complimentary. Farmer & Henley, Partridge and Green have Dublin dissector, Dublin packet, Dublin trick and Dublin rules, but no knight. A search of the internet produces thousands of references to a song, whose lyrics I have perused but which doesn't appear to be relevant.

Answer 1

jwpat7's answer seems spot-on as to exactly what a "Dublin Castle knight" is - although I'd add that the meaning is probably clearer if you read it as "a knight of Dublin Castle", rather than "a castle knight of Dublin".

I'd like to address, however, why all of the definitions you listed seem to have negative (or at least not-very-positive) connotations. The English and the Irish have been "bosom enemies" for hundreds if not thousands of years; the English occupied and ruled Ireland until 1922 - and Dublin (Dublin Castle in particular) was the administrative center of that occupation. To an English speaker, referring to something as "Dublin (whatever)" would tag it as stereotypically Irish; to an Irish speaker, calling something "Dublin (whatever)" would tag it as collaborationist. In either case, the intent might well be pejorative.

Answer 2

Near the middle of Chapter 12 of dublincastle.ie's History of Dublin Castle we find:

The 'Illustrious Order of St. Patrick' was the Irish equivalent of the English 'Order of the Garter' and the Scottish 'Order of the Thistle'. Knights were required to be 'descended of three descents of nobleness' on both paternal and maternal sides. Its purpose was to give social advancement to senior peers and so, further secure their loyalty. An award of Knighthood was seen as evidence of the high social standing of the recipient and there was considerable competition for the limited places.

That is, a Dublin Castle Knight was elite and honorable. However, the Illustrious Order of St. Patrick no longer exists, having come to an end in 1922, if I correctly understand wikipedia's Dublin Castle article. Edit: As noted in the Knights of St. Patrick article [the article mentioned in Henry's comment], regular creation of knights of Saint Patrick ceased in 1921, with only four knights appointed after that. All of the 130 Knights of St. Patrick were indeed royals or peers, as noted in the comment. It is not perfectly clear to me whether the 20 or so Barons among the Knights could properly be addressed by the title Sir. Wikipedia shows My Lord / Your Lordship for address of a Baron Lord of Parliament and Sir for address of a Scottish feudal baron or address of a Baronet [which is "above all knighthoods except for the Order of the Garter and, in Scotland, the Order of the Thistle"].