decoction

An extraction or essence of something, obtained by boiling it down.

[I]nſtead of Honey, Rob of Elder, Conſerve of Roſes, or Syrup of Violets; Glyſters, Pedilavia of emollient Decoctions with Nitre; or Elder, Vinegar, or Focus's of the ſame, applied with Sponges behind the Ears, to the Armpits, Groins, Hams, &c. or with Barley-water and a little Roſe-vinegar.

The transition is a keen one, I assure you, from a schoolmaster to a sailor, and requires a strong decoction of Seneca and the Stoics to enable you to grin and bear it.

The process of boiling something down in this way.

Even the fixed principles of vegetables, at least some of them, are injured by long decoction. The extractive matter, for instance, gradually absorbs oxygen from the atmosphere, and is converted into a substance nearly insipid and inert.