impracticable
1. [ adjective ] not capable of being carried out or put into practice
Synonyms: unfeasible unworkable infeasible
Examples:

"refloating the sunken ship proved impracticable because of its fragility" "a suggested reform that was unfeasible in the prevailing circumstances"

Related terms: impossible
Similar spelling:   impracticably
  impractical
  impracticability
  impracticality