phlegmatic

Not easily excited to action or passion; calm; sluggish.

Calm and phlegmatic, with a clear eye, Mr. Fogg seemed a perfect type of that English composure which Angelica Kauffmann has so skilfully represented on canvas.

2013, A.O. Scott, “How It Looks to Think: Watch Her,” Rev. of Hannah Arendt, dir. by Margarethe von Trotta, New York Times 29 May 2013: C1. Print. Their friendship (immortalized in a splendid volume of letters that has clearly served as one of Ms. von Trotta's sources) is a fascinating study in cultural and temperamental contrast, an impulsive and witty American paired with a steady, phlegmatic German.

Generating, causing, or full of phlegm.

cold and phlegmatic bodies

Near-synonyms: phlegmish, phlegmy

One who has a phlegmatic disposition.