The Collaborative International Dictionary
subcalibre
Subcaliber \Sub*cal"i*ber\, a. Smaller than the caliber of a firearm. [Written also subcalibre.]
Subcaliber projectile, a projectile having a smaller
diameter than the caliber of the arm from which it is
fired, and to which it is fitted by means of a sabot.
--Knight.
Wiktionary
subcalibre
a. (alternative form of subcaliber English)