Student or Learner
"The ill-advised course of action ended up costing the company millions of dollars"
Why does it say "ill-advised"? Isn't "ill" supposed to be an adjective? If adjectives can be used there then is it possible to replace that word with bad-advised or poor-advised?
You can be ill-advised or well-advised. As bhaisahab said, the word is a compound adjective. Normally how you were advised would be followed by an adverb.
I was advised well.
I was advised badly.
However, we can change the word order:
I was well advised.
I was badly advised.
I got good advice.
I got bad advice.
If we want to use them as compound adjectives:
That was a well-advised plan.
That was an ill-advised plan.
I can't give you a good explanation as to why well/good become "well-advised" but badly/bad become "ill-advised" but the fact remains that that is how it works.