adder In its simplest form, a digital electronic device that performs the operation of addition on two binary digits, the augend and the number to be added, the addend. It is therefore also known as a binary adder. This operation is exemplified by the truth table shown in the diagram, where Σ is the sum and C_o is the carry. From this it can be seen that binary addition may generate a carry to subsequent stages.

A full adder has provision for inputs of addend, augend, and a carry bit and is capable of generating sum and carry outputs. These adders may be cascaded when it is desired to add binary words greater than one bit in length by connecting the carry inputs of each stage to the carry output of the previous stage.

A half-adder is an implementation of an adder that has provision only for input of addend and augend bits and is capable of generating sum and carry outputs. These devices cannot directly be cascaded as can full adders but may be made to perform a similar function by including additional logic gating.

See also parallel adder, serial adder, carry lookahead.

adder the only venomous snake in Britain; in biblical and classical translations, adder is often used as the word for a poisonous snake.

In Old English, the form of the word was nædre ‘serpent, adder’, of Germanic origin. The initial n was lost in Middle English by wrong division of a naddre (compare apron, auger).

See also deaf as an adder.

ad·der / ˈadər/ • n. a small Eurasian viper (Vipera berus) that has a dark zigzag pattern on its back and bears live young. ∎  used in names of similar or related snakes, e.g., puff adder.

adder †serpent; viper. OE. nǣd(d)re, corr. to OS. nādra, OHG. nātara (G. natter) and (with a different vowel-grade) ON. naðr(a), Goth. nadrs; rel. to L. natrix water-snake. As in apron, auger, umpire, orig. n- has been lost by coalescence with a preceding indef. art., a nadder becoming an adder (XIV). For the reverse process see NEWT, etc.

adder Any of several snakes in various parts of the world, some poisonous and others harmless. The European viper (Vipera berus) is called an adder in Britain. The puff adder (Bitis arietans) is a large African viper, and the death adder (Acanthophis antarticus) is a dangerous Australian elapid.