CAPTAIN-Lieutenant, he who, with the rank of captain, but the pay of lieutenant, commands a troop or company in the name and place of some other person who is dispensed with, on account of his quality, from performing the functions of his post.
Thus the colonel being usually captain of the first company of his regiment, that company is commanded by his deputy under the title of Captain-Lieutenant.
So in England, as well as in France, the king, queen, dauphin, princes, &c. have usually the title of captain of the guards, gens d'armes, &c. the real duty of which offices is performed by captain-lieutenants.