Unfeasible (adjective)

1. Not feasible; not able to be done or carried out successfully.
2. Not practical or possible to accomplish.

Origin:

Mid 19th century: from un-1 + feasible, on the pattern of words such as impossible.

Examples:

1. The plan was unfeasible and had to be abandoned.
2. The project was deemed unfeasible due to lack of funding.
3. The idea was unfeasible and had to be modified.
4. The proposal was unfeasible and was rejected.
5. The demand was unfeasible and could not be met.