(~s)
1.
A ~ is someone whose job is to taste different wines, teas, or other foods or drinks, in order to test their quality.
...a wine ~.
N-COUNT
2.
If you refer to something as a ~ of something greater, or of something that will come later, you mean that it gives you an idea what that thing is like, and often makes you interested in it or want more of it. (mainly BRIT; in AM, usually use taste )
The book is essentially a ~ for those unfamiliar with the subject.
N-COUNT: usu sing, oft N of n