Aboard and abroad 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.
Aboard is a verb. It means to climb onto a flying, sailing, or other traveling vessel, and stay there. When you hear “All aboard” it’s a signal to passengers, “if you bought a ticket you better be on the vessel or boarding in the next 5 minutes because we’re leaving.”
Abroad is an preposition. It means areas very distant from your point of origin. For example, when a high school or college student studies “abroad,” they travel to another country to live with another family for a year or a portion of a year. The student is in the other country to experience what school, and day to day life is like in that country, and often to improve their foreign language skills.
The following story uses both words correctly:
After high school, Aleksei wanted to travel abroad, but his parents wanted him to stay home and run the family dairy. It was his inheritance; he knew he should be grateful, but it wasn’t the life he wanted. Very early one spring morning, he got up early and trekked miles to the nearest port. No one saw him climb aboard a merchant vessel, headed he wasn’t sure where.