Yes it is one word.
frantic
Infertile is the word that means unable to have children.
That is the correct spelling of "indivisible" (unable to be divided).
intransigent
Unable is an adjective.
An anagram of "unable" is the word nebula.
The word unable is an adjective, and has no plural.
barren
The words for unable to be fixed are uncorrectable, irremediable, irreparable, or incurable.The word for unable to be "corrected" (as in made to conform) is incorrigible.
Another common word for can't is the word "unable". To be unable is the act of not being able to accomplish a task.
unable to ambulate well.
The word for someone who is unable to read or write is "illiterate."