Yes, indestructible is a word. It means incapable of being destroyed.
Illegible.
unalienable
The opposite of the word capable is incapable.
my best guess is permanent
"Incompetent" means lacking the necessary ability, skills, or qualities to perform a task or job effectively. It suggests an inability to carry out duties or responsibilities in a satisfactory manner.
No, "uncapable" is not a prefix. It is a word that combines the prefix "un-" meaning "not" with "capable" to form a word that means "not capable."
indescribableIneffable. -adjective 1. incapable of being expressed or described in words; inexpressible: ineffable joy.
He was incapable of performing even the most trivial task.
Audible."inaudible" quite literally means "incapable of being heard"; by stripping the prefix "in-", you get the word "audible", which indeed means "capable of being heard".
immobile paralyzed
No one could change or improve the girl's incorrigible behavior.