Crossword Genius

A condition mostly intrinsic — extremely unstable (7)

Ross

I believe the answer is:

astatic

I'm a little stuck... Click here to teach me more about this clue!

But I can't explain it at all! Could you help me understand?

(Other definitions for astatic that I've seen before include "move about" , "without determination or polarity" , "unable to stay still?" .)

I've seen this clue in The Hindu.
Want a hint initially instead of a full solution? Install my app