Capitol

[kap-i-tl] /ˈkæp ɪ tl/
noun
1.
the building in Washington, D.C., used by the Congress of the U.S. for its sessions.
2.
(often lowercase) a building occupied by a state legislature.
3.
the ancient temple of Jupiter at Rome, on the Capitoline.
4.
the Capitoline.
Origin
1690-1700, Americanism; < Latin capitōlium temple of Jupiter on Capitoline hill, Rome, taken to be a derivative of caput head; replacing Middle English capitolie < Old North French
Can be confused
capital, Capitol (see usage note at capital)
Usage note
See capital1.
British Dictionary definitions for Capitol

Capitol

/ˈkæpɪtəl/
noun
1.
  1. another name for the Capitoline
  2. the temple on the Capitoline
2.
the Capitol, the main building of the US Congress
3.
(sometimes not capital) Also called statehouse. (in the US) the building housing any state legislature
Word Origin
C14: from Latin Capitōlium, from caput head
Word Origin and History for Capitol
n.

"building where U.S. Congress meets," 1793 (in writings of Thomas Jefferson), from Latin Capitolium, temple of Jupiter Optimus Maximus on the Capitoline Hill in ancient Rome. Used earlier of Virginia state houses (1699). Its use in American public architecture deliberately evokes Roman republican imagery. With reference to the Roman citadel, it is recorded in English from late 14c., via Old North French capitolie. Relationship of Capitoline to capital is likely but not certain.