[kal'i-ber]. A mind of no calibre: of no capacity. A mind of great calibre: of large capacity. Calibre is the bore of a gun, and, figuratively, the bore or compass of one's intelligence.
“The enemy had generally new arms ... of uniform caliber.”—Grant: Memoirs, vol. i. chap. xxxix. p. 572.
“We measure men's calibre by the broadest circle of achievements.” —Chapin: Lessons of Faith, p. 16.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894