The phrase, "ill adapted to" means not well conformed or not well changed or not suitable to the new situation. The word "ill" has the meaning of "not" in this context. Adapt means to conform or to change, so when put together, the phrase means not changed or not conformed to the new circumstance.

What does being adapted mean?

1 : the act or process of changing to better suit a situation. 2 : a body part or feature or a behavior that helps a living thing survive and function better in its environment. adaptation.

What is the definition for ill-suited?

: poorly suited : not having the qualities that are right, needed, or appropriate for something a pet ill-suited for travel ill-suited for this job.