Err and Heir 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 sees what you are typing and anticipates what word, or words it could be. Sometimes it’s correct, many times it couldn’t be more wrong.
Err is a verb. It means to make a mistake, or screw up somehow. Have you ever heard the phrase “to err is human, to forgive divine”? It means that everyone makes mistakes, not everyone forgives mistakes, but if you do, you demonstrated the better parts of your nature by doing so.
Heir is a noun. It relates to a monarchy or family property. An heir is the prince, or princess, in line for a throne. In a family, when an older relative dies, his/her will states which younger family members will receive money or property from his/her estate.
The following story uses both words correctly:
Twins Hermes and Hermione waited anxiously as their mother’s will was read aloud. Hermes assumed he was the heir getting everything, Hermione felt he erred in his logic and overconfidence.
This post is related to another post: Easily Confused Words: Air vs. Err