Product of Seagrams, one may relieve stress (8)

'product' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

'seagrams one may relieve stress' is the wordplay.
I cannot really understand how this works, but
an anagram of 'seagrams' is 'massager' which is present in the answer.
No letters remain.
This may be the basis of clue (or it may be nonsense).

'of' is the link.

Can you help me to learn more?