English Reference
noun

adder

n.
US /ˈædɝ/ UK /ˈædɐ/ adder

  1. 01 B2 Upper Intermediate British English

    a small poisonous snake, often with a dark zigzag pattern on its back.

    the common European viper (Vipera berus), noted for being the only venomous snake native to Britain.

    Simple

    We saw a small adder sunning itself on a rock during our hike.

    In context

    The adder is generally shy and will only strike if it feels cornered or is accidentally stepped on by a hiker.

    Usage

    In North America, the term is sometimes applied to other non-venomous snakes like the milk snake.

  2. 02 C1 Advanced Technical Computing

    a person who adds numbers, or a machine or computer part that does addition.

    a person who performs arithmetic addition, or a digital circuit that calculates the sum of numbers.

    Simple

    The computer uses a high-speed adder to process the math problems.

    In context

    A full adder is a fundamental component of a central processing unit, capable of handling carry bits from previous operations.

  3. 03 C2 Proficiency InformalSlang

    a person who has attention deficit disorder (ADD).

    a person diagnosed with or exhibiting symptoms of attention deficit disorder.

    Simple

    As an adder, he finds it helpful to use a timer to stay focused on his work.

    In context

    The support group provides a space for adders to share strategies for managing executive dysfunction in a professional environment.

    Teacher's tip

    This is a niche slang term derived from the acronym ADD; it is not a standard medical term and may be confusing to those unfamiliar with neurodiversity slang.

There is no organic matter left." He added: "Things like the snakes, adders, reptiles, they can not escape, so they will be destroyed.

BBC News· 7 Aug 2026

Etymology 1

From Middle English nadder, addere, rebracketing of “a naddere” as “an addere”, from Old English nǣdre (“snake”), from Proto-West Germanic nadrā, from Proto-Germanic nadrǭ, from pre-Germanic néh₁treh₂, variant of Proto-Indo-European n̥h₁trih₂, from *(s)neh₁- (“to spin, twist”). See also West Frisian njirre, Dutch adder, German Natter, Otter; also Welsh neidr, Latin natrīx (“watersnake”), Dutch naaien.

Etymology 2

From add + -er.

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

This entry
Origin ine-pro *n̥h₁trih₂
Level C2 · Proficiency
Frequency Occasional
Updated