What is another way to express something that is idempotent?

I understand the word "idempotent" to describe an action where the second time that action is applied, it has no additional effect. In other words, redundant operations have no effect.

The first usage of the word seems to have been made in a mathematical context, but it is also widespread in computer science (see usage here). As a computer science student this terminology is very useful, but it can also feel odd saying the word. There are even stackexchange questions asking how to pronounce it!

I'd like to be able to express the meaning of the word idempotent in a casual setting using only one word without sounding too technical (a two-word solution may also be interesting).

I tried to find synonyms in a dictionary but found none. I tried to translate to other languages to see if I could adopt a new word, but I couldn't find one.

As a last resort, I don't mind if I have to create my own word or phrase. I was thinking of saying something has "null redundancy". Maybe I could shorten it to be "nullred", but that sounds silly.

Sample Sentence

A credit card transaction should be < word > so that you don't get charged twice.

Another example

Instead of saying "It doesn't do anything the second time", shorten to "It isn't < word >"

I don't care whether the word is a noun, verb, or adjective as long as it makes sense. I think it is best suited as a noun and adjective though.

TL;DR

Do any synonyms of the word idempotent actually exist?

Using latin roots or some other method, can you make a substitute word that you think makes sense?

Solution 1:

There is a level of ambiguity in this question. It it the physical act of making transactions that should not be repeated—or is it the charge being applied against the card (regardless of the number of transaction attempts) that should not be repeated?

Multiple Card Swipes

The most idiomatic way of saying it would be:

A credit card transaction should not be repeated so that you don't get charged twice.

But that uses a three-word verbal phrase.

Merriam-Webster defines the adjective unrepeated:

: not repeated

As such, the sentence could be phrased:

A credit card transaction should be unrepeated so that you don't get charged twice.

Although unrepeated is an actually defined word that nobody would misunderstand, it doesn't sound as normal as not to be repeated.

If it's not a problem forming a word from the normal rules of syntax, you could take the prefix non and apply it to the more normal adjective repetitive:

A credit card transaction should be nonrepetitive so that you don't get charged twice.

While I don't find nonrepetitive in Merriam-Webster or Oxford (at least in their online version), it does exist in more minor dictionaries such as The Free Dictionary and Vocabulary.com.

Multiple Bank Charges

To mirror the previous sense, the most idiomatic way of saying this would be:

A credit card transaction should not be accruable so that you don't get charged twice.

From Merriam-Webster's definition of the verb accrue, from which accruable is formed:

3 : to accumulate or be added periodically
// interest accrues on a daily basis

Various websites use the word nonaccrual; for instance, Investopedia defines nonaccrual loans.

As such, it's not a stretch to think that the single-word form of the adjective to use in this sense could be nonaccruable:

A credit card transaction should be nonaccruable so that you don't get charged twice.