So "der verein" absolutely cannot be translated as "the union"??
LEO German-English Dictionary gives "union" as one of the translation for "verein"
What is the reason 'Verein' has an 's' at the end of it? The noun is stated to be singular, so it can't be an alternate plural form.
I think it has something to do with 'des' (is it genitive form?)
It is genitive singular of a masculine noun 'der Verein'
In the genitive case, masculine and neuter nouns have an "s" or "es" on the end. So "des Vereins", "des Mannes".