smack v. smack of sth : slight flavour of sth お尻ぺんぺんも同じスペル。
I think it would normally be the plural "smacks of" http://dictionary.reference.com/search?q=smacks "A distinctive flavor or taste. A suggestion or trace." I'm not sure it's a great translation though.
I was wrong. I mixed up the lines for v with that of n. It is for n-explanation but it should be used in singular according to an OXFORD dictionary. In contect "smack" is V after "This soup". いい訳に見えるけど。
Appeared in JLPT 2 (Select particle, が)
Not sure if the issue is resolved, but the phrase is always "X smacks of Y". Its a good enough translation, though, as a native speaker i can say this phrase has become _slightly_ archaic.