Impatient and inpatient are easily confused words.
The spell-check application of most word processing software programs would not catch a slip-up of these two words. Spell-check is looking for words that aren’t in its dictionary, and words that resemble words in its dictionary but are possibly spelled wrong. Spell-check isn’t perfect. It doesn’t know and can’t guess what word you wanted or what word you meant, it can only judge the words on the page. If you used words that are all spelled correctly, it gives you a pass anyway.
Autocorrect suggests words that start with the same letters. It suggests what word you may want to save time, but quite often, its suggestions couldn’t be more off base and produces humorous results.
Impatient is an adjective. It means someone who cannot wait for anything without getting mad, irritated, complaining, or fidgeting.
Inpatient is a noun. It means someone residing at the hospital awaiting care or a procedure.
The following story uses both words correctly:
Imogen learned that she had sleep apnea and she required a tonsillectomy. It would be an inpatient procedure so they could monitor her breathing until the swelling had gone down. She hated hospitals, and she just knew she’d be impatient with everyone involved until the whole ordeal was over.