Correct spelling


Correct spelling, explanation: the base form of undecidable is to decide. The origin of both words can be found in decider, which was a Latin word meaning to determine. Undecidable appeared in English in the Middle Ages together with a noun – decision.

Definition of undecidable:
1. adjective – when something seems to be really difficult to solve, e.g. a problem,
His paintings are some abstract, undecidable creatures so I have no idea what he tries to convey with his art.

Collocations with undecidable:
A few common collocations include: undecidable case, undecidable issue, and undecidable task.
The algorithm became so complex that the understanding of this program is an undecidable case.
Moral questions are often undecidable issues, which vary depending on the person.
I hadn’t prepared much for my final exams so a lot of tasks seemed to be undecidable to me.

Incorrect spelling


Incorrect spelling, explanation: undecidable joins the prefix -un with the root word, which is decide, and the suffix – able. However, it’s worth remembering that when we add the -able ending, we need to remove the -e letter from decide. Therefore the correct spelling is not undecideable – as a number of English users think – but undecidable.