# cons

/ˈkɑnz/ (US) · /kˈɒnz/ (UK)

Source: https://englishreference.com/word/cons
Updated: 2026-06-20

## Senses

### 1. disadvantages

noun · CEFR B1

the negative points or disadvantages of an idea or plan.

For teachers: the arguments or factors against a particular proposition or course of action.

- We need to weigh the pros and cons before we decide to move house.
- The committee spent hours debating the pros and cons of the proposed merger, focusing specifically on long-term financial stability.

### 2. programming data structure

noun · CEFR C2 · Technical

a basic building block in some computer languages used to hold two pieces of data together.

For teachers: a fundamental data structure in Lisp and related functional languages, consisting of a pair of pointers (traditionally car and cdr).

- In Lisp, a list is actually a series of cons cells linked together.
- The function returns a new cons whose first element is the input value and whose second element is the existing list.

### 3. to add to a list

verb · CEFR C2 · Technical

to add a new item to the beginning of a list in computer programming.

For teachers: to prepend an element to a list by creating a new cons cell; the standard method of list construction in functional programming.

- You can cons the new ID onto the front of the user list.
- The algorithm efficiently conses each discovered node onto the accumulator to build the result set in linear time.

Usage: The verb is transitive and typically takes the element being added as the object.

## Examples

- We need to weigh the pros and cons before deciding.
- The committee spent the afternoon listing the cons of moving the headquarters to a more expensive city.
- While the technological benefits of the upgrade were clear, the financial cons proved too significant for the board to approve the expenditure this quarter.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.