AD. A Latin preposition, signifying to. It is probably from Heb. Ch. Syr. Sam. Eth. and Ar. To come near, to approach; from which root we may also deduce at. In composition, the last letter is usually changed into the first letter of the word to which it is prefixed. Thus for adclamo, the Romans wrote acclamo. The reason of this change is found in the ease of pronunciation, and agreeableness of the sounds.

AD hominem, to the man, in logic, an argument, adapted to touch the prejudices of the person addressed.

AD inquirendum, in law, a judicial writ commanding inquiry to be made.

AD libitum [Latin] at pleasure

AD valorem, according to the value, in commerce and finance, terms used to denote duties or charges laid upon goods, at a certain rate per cent, upon their value, as stated in their invoices; in opposition to a specific sum upon a given quantity or number.