Impalpable (adjective)

1. Impossible to touch or feel; not tangible.
2. Difficult to understand or grasp; not clear or distinct.

Origin:

Early 17th century: from latin impalpabilis, from in- "not" + palpabilis "tangible".

Examples:

1. The evidence was impalpable, making it difficult to build a case.
2. The impalpable nature of the gas made it difficult to detect.
3. His impalpable argument left the audience confused.
4. The impalpable mist made it difficult to see more than a few feet ahead.
5. The impalpable feeling of anxiety made it hard for her to focus.