1560s, "degree of merit or relevance," a figurative use from Middle French calibre (belated 15c.), evidently in the end from Arabic qalib "a mold for casting." Arabic in addition used the term into the sense "mold for casting bullets," the oldest literal meaning in English. Indicating "inside diameter of a gun barrel" is attested from 1580s. Barnhart remarks that Spanish calibre, Italian calibro "appear too late to act as intermediate types" amongst the Arabic word therefore the French.
diameter of a tube or gun-barrel
- a degree or quality of excellence or really worth
- Alt. of Calibre