Harry Potter and the Half-Blood Prince
Chapter 7: The Slug Club
Where a Vietnamese word has been borrowed from Chinese, the original Chinese character is shown in parentheses.
The 'Slug Club' is a circle of students collected by Horace Slughorn (see Chapter 4). It is an exclusive little coterie as Professor Slughorn prefers to hobnob with well-connected students or students likely to do well in their later careers. The name derives from the first part of Slughorn's surname, 'Slug', which also happens to refer to a slimy wormlike gastropod, like a snail without a shell, that comes out at night to feed.
Although Slughorn himself uses the name 'Slug Club' affectionately, it doesn't sound particularly flattering. The name conjures up a picture of Slughorn as a large fat slug, or of the members as being slug-like, with connotations of sliminess or 'despicable, morally reprehensible'. There is also a connection with 'sluggard'.
A more detailed discussion of how this pun is treated (along with a grading of 'Pass' or 'Fail') is found at Slughorn, Slug Club, Sluggish.
As I have mentioned elsewhere, the word for 'club' is a convoluted borrowing. It appears originally to have been a Japanese attempt to render the English word 'club' in Chinese characters, as 倶楽部, pronounced kurabu. It was then borrowed into Chinese as 俱樂部 / 俱乐部 jùlèbù. Vietnamese borrowed this, presumably when Vietnamese still used Chinese characters, as câu lạc bộ. Japanese seldom uses 倶楽部 nowadays, preferring katakana クラブ kurabu.