A word I found in a paper (”Graph optimization problems are known to be intractable”) and that seems very close to french.

intractable  (n-trkt-bl)
adj
1. Difficult to manage or govern; stubborn. See Synonyms at unruly.
2. Difficult to mold or manipulate: intractable materials.
3. Difficult to alleviate, remedy, or cure: intractable pain.