opposable

/əˈpoʊzəbəl/
adjective
  1. (of a thumb or digit) Capable of being placed opposite the other fingers to grasp or hold something.
    • Humans have opposable thumbs, which allow us to write and use tools.
    • Many primates have opposable big toes for climbing trees.
    • The koala has two opposable thumbs on each front paw for gripping branches.
  2. Able to be resisted or argued against.
    • The court ruled that the decision was opposable and could be challenged.
    • The new policy is opposable by anyone who disagrees with it.
    • In a democracy, every law is opposable through legal means.