D defs.my
Entry 1 sense Webster, 1913

Rotunda

/rōt-ŭn'-də/ · Ro·tun·da · IPA /ɹoʊˈtʌndə/
01 n. A round building; especially, one that is round both on the outside and inside, like the Pantheon at Rome. Less properly, but very commonly…
  1. 1.
    A round building; especially, one that is round both on the outside and inside, like the Pantheon at Rome. Less properly, but very commonly, used for a large round room; as, the rotunda of the Capitol at Washington.(Arch.)