lack of ability (especially mental ability) to do something
"His inability to understand the complex instructions prevented him from completing the task alone."
Lack of the ability to do something; incapability.
"His inability to lift even a light backpack surprised everyone who had seen him carry heavy luggage before."
In plain English: Inability is when you simply cannot do something because of a lack of skill, strength, or opportunity.
"His inability to speak Spanish made traveling difficult for him."
Usage: Use "inability" as an uncountable noun when referring generally to a lack of skill or capacity, rather than counting specific instances like you would with countable nouns such as "errors." It is often paired directly with infinitive verbs (e.g., inability to swim) without requiring the preposition "of," which distinguishes it from similar terms that might require different grammatical structures.
The word inability comes from the combination of in- and ability, originally meaning disqualification for an official position before evolving to describe a general lack of capacity. It entered English through earlier forms like inhability that were equivalent to these two parts.