Kettledrum

n.
  1. (Mus.) A drum made of thin copper in the form of a hemispherical kettle, with parchment stretched over the mouth of it.
  2. An informal social party at which a light collation is offered, held in the afternoon or early evening. Cf. Drum, n., 4 and 5.

Kettledrums, in pairs, were formerly used in martial music for cavalry, but are now chiefly confined to orchestras, where they are called tympani.