intractable

adjective
  1. 1

    Not tractable; not able to be managed, controlled, governed or directed.

  2. 2

    (of a mathematical problem) Not able to be solved.

  3. 3

    (of a problem) Difficult to deal with, solve, or manage.

  4. 4

    (of a person) Stubborn; obstinate.

  5. 5

    Difficult to treat (of a medical condition).

Source: https://en.wiktionary.org/wiki/intractable