Etymology Dictionary

CALIBER, CALIBRE,  the size of the bore of a gun.  (F.)   The form calibre is closer to the French, and perhaps now more usual.   Caliber occurs in Reid's Inquiry, c. 6. s. 19 (R.)   Neither form appears to be old.  We also find the spellings caliver and caliper in Kersey's Dict. ed. 1715.—F. calibre, said to have been 'introduced in the 16th century from Ital. calibro;' Brachet.   Cotgrave has:  'Calibre, a quality, state, or degree;' also:  'Qualibre, the bore of a gun, or size of the bore, &c.   Il n'est pas de mon qualibre, he is not of my quality, ranke, or humour, he is not a fit companion for me.'   β. Of uncertain origin.   Diez suggests Lat. quá librá, of what weight, applied to the bore of a gun as determined by the weight (and consequent size) of the bullet.   See Librate.   γ. Littré suggests quite a different origin, viz. Arab. kálib, a form, mould, model; cf. Pers. kálab, a mould from which anything is made; Rich. Dict. pp. 1110, 1111.   Der. calipers, q.v.; also caliver, q.v.